How to Install a Toilet: A Step-by-Step Guide That Actually Works

How to install a toilet looks intimidating until you watch one done in 45 minutes. Two bolts hold the porcelain to the floor, one wax ring seals the drain, one supply line carries the water. The rest is muscle memory and patience. This guide covers the full swap, including the flange checks and leak-test steps most quick tutorials skip. See also the wax-ring replacement guide, how to measure your rough-in.

How to install a toilet: the 45-minute walkthrough

The four things people skip

The single most-skipped step: turn the water off at the wall, flush, hold the handle down to drain the tank, then disconnect the supply line BEFORE you do anything else. Skip any of those four and you’ve got water on the floor. A standard install takes a confident DIYer 60 to 90 minutes. The toilet itself weighs about 80 to 100 pounds. You can lift it, but lift the tank and the bowl separately if you can.

What you’ll need (most installs):

• A new toilet (bowl + tank, or one-piece)
• A new wax ring sized to your flange (standard or extra-thick)
• Two new closet bolts with washers and caps
• A flexible braided steel supply line (3/8″ compression x 7/8″ ballcock, usually 12″)
• Adjustable wrench, channel-lock pliers, a small level, a putty knife
• A bucket, a sponge, and two old towels
• Optional but recommended: rubber gloves, knee pads, blue painter’s tape, 100% silicone caulk

Time required: 60 to 90 minutes for a swap into an existing flange. Add 30 minutes if you’ve never done it. Add a full afternoon if the flange is broken or the floor is soft. See when to call a plumber.

Start here: Before you buy anything, measure the rough-in. That’s the distance from the finished wall behind the toilet to the center of the closet bolts (not the wall to the back of the bowl). Twelve inches is standard. Ten and fourteen exist. Buy a toilet that matches.

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What you need (the full list, with notes) {#what-you-need}

A toilet swap is mostly a parts game. If you have the right pieces on the floor before you start, the install itself is fast.

Hardware and parts:

• New toilet: one-piece or two-piece, in the correct rough-in size (10″, 12″, or 14″)
• Wax ring: standard for a flush flange, extra-thick or doubled if your flange sits below the finished floor. Korky and Fluidmaster both make solid ones. Waxless alternatives like the Korky NeverLeak or Fluidmaster Better Than Wax exist and are forgiving of imperfect installs, especially for first-timers.
• Two new closet bolts: usually 1/4″ x 2-1/4″ brass. New ones every time. They’re a dollar.
• Brass washers + plastic caps: usually come bundled with the bolts
• Flexible braided stainless supply line: 3/8″ compression on the valve end, 7/8″ ballcock nut on the tank end. The standard length is 12″; measure if your shut-off is unusually placed.
• 100% silicone caulk: clear or white, for the base. Plumber’s putty in the can is for sink drains, not toilet bases. Do not substitute.

Tools:

• Adjustable wrench (8″ minimum)
• Channel-lock pliers
• A small torpedo level
• A 4-in-1 screwdriver
• A utility knife
• A putty knife or 5-in-1 scraper
• A small hacksaw (in case old bolts won’t budge)
• A bucket, a sponge, two old towels

Optional:

• Rubber gloves (the inside of an old toilet has been wet for a decade)
• Knee pads (your knees will thank you)
• Blue painter’s tape (for marking the bolt positions and protecting porcelain)
• A second pair of hands for the lift

If you’re swapping a toilet, also have a heavy-duty contractor garbage bag ready. You’ll want to bag the old one immediately. They drip.

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Before you start: the five-minute assessment that saves an hour later {#before-you-start}

Do not skip this. Most install disasters trace back to something visible before the first wrench turn.

Measure the rough-in

The rough-in is the distance from the finished wall (not the baseboard, not the trim) to the center of the closet bolts on the floor. Twelve inches is the standard in almost every house built since the 1970s. Older homes, especially East Coast ones built before 1960, sometimes have 10″ or 14″ rough-ins. A toilet meant for 12″ will not fit a 10″ rough-in. It will hit the wall.

Inspect the old flange

The closet flange is the plastic, brass, or cast iron ring screwed to the floor with the drain pipe coming up through it. Pull the old toilet (Steps 1–2 below) and look at it carefully:

• Is it cracked? A cracked PVC flange is the single most common hidden problem in a toilet swap. It must be replaced or repaired with a flange repair ring before you set the new toilet.
• Are the slots intact? The two slots on opposite sides are where the closet bolts sit. If one is broken off, you need a repair ring or a new flange.
• Is it at the right height? The flange should sit flush with the finished floor (or slightly above it). If it’s recessed below the floor by more than a quarter inch, use an extra-thick wax ring, double up, or use a flange extender.
• Is it secure to the floor? Press down on it. If it rocks or lifts, the screws have failed and the subfloor underneath is likely rotten.

Check the floor

Press hard on the floor in a ring around the flange. Spongy, dark, or stained subfloor under an old toilet is the second-most-common surprise. If the floor moves, the install is on hold. You have a subfloor repair before you have a toilet install. This is also the time to look for asbestos floor tile (small 9″ tiles in older homes) or lead bend joints. Both are stop-and-call-a-pro moments.

Decide: full replacement, or fresh install?

If there’s no toilet there yet (new bathroom, gut renovation), you skip Steps 1 and 2 and start at Step 3. Otherwise, work all the way through.

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Step 1: Turn off the water and drain the tank {#step-1-water-off}

The water shut-off valve sits on the wall behind the toilet, near the floor: an oval handle, sometimes a small lever. Turn it clockwise until it stops. If it spins freely or won’t move, that valve is failing. Replace it now while the toilet is out; it’s a fifteen-minute job and a lot easier without a bowl in the way.

Then:

1. Flush the toilet and hold the handle down to drain as much tank water as possible.
2. Sponge out the remaining water in the tank and the bowl. A wet/dry vac is faster if you have one.
3. Lay a towel under the supply line before disconnecting.

The bowl will still hold an inch or two of water in the trap. You can’t sponge it out. Just be ready for it when you tip the toilet later.

Warning: Don’t trust the shut-off until you’ve flushed and seen the tank stay empty. Old valves fail closed and open. If water keeps trickling in, shut the house main and replace the valve before continuing.

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Step 2: Disconnect the supply line and remove the old toilet {#step-2-remove-old}

If the nut spins off cleanly, your day is going well. If the bolt spins with the nut because it’s rusted into one piece, cut it with a small hacksaw between the bolt and the porcelain. A reciprocating saw with a metal blade works too, carefully.

1. Unscrew the supply line nut from the bottom of the tank by hand or with channel locks. Catch the drip in your towel.
2. Pop the caps off the closet bolts at the base of the toilet with a utility knife or 5-in-1 scraper.
3. Unscrew the closet bolt nuts. Two scenarios:
4. For a two-piece toilet, remove the tank first. Two or three bolts hold the tank to the bowl from inside the tank. Take them out, lift the tank straight up, set it on a towel.
5. Rock the bowl gently to break the wax seal. It’ll feel stuck for a second, then release with a small sucking sound.
6. Lift the bowl straight up and walk it to your garbage bag or out to the curb. Old wax will fall off as you go. Towels.

Now you’re looking at a hole in the floor with a flange around it. Stuff a rag into the drain pipe immediately. Sewer gas is unpleasant, and so is dropping a closet bolt into the pipe.

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Step 3: Clean the flange and check it’s solid {#step-3-clean-flange}

Scrape every bit of old wax off the flange with a putty knife. All of it. New wax does not adhere through old wax. That’s the single most common cause of a base leak two weeks later.

Then check:

• Flange height: within 1/4″ of flush with the finished floor is ideal. Below that, use an extra-thick wax ring or a flange extender.
• Flange screws: there should be four screws holding it to the subfloor. If any are missing or stripped, drive new stainless screws into solid wood.
• No cracks, no broken slots: if the flange is damaged, install a metal repair ring before going any further.

Pull the rag out of the drain pipe only when you’re seconds away from setting the bowl. Until then, keep it stuffed.

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Step 4: Install the new closet bolts {#step-4-closet-bolts}

Slide the two new brass closet bolts into the slots on the flange, threads pointing up. The slot lets you slide the bolts toward the front or back of the flange to align with the toilet.

The bolts must be exactly opposite each other, perpendicular to the wall behind the toilet. A bolt off-center by half an inch will make the bowl sit crooked, and a crooked bowl rocks.

Slip the small plastic or metal alignment washers (included with the bolts) down over the threads to keep the bolts upright. They’ll fall over while you set the bowl otherwise. Annoying, not fatal. Some installers also wrap a small piece of painter’s tape around each bolt to hold it vertical.

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Step 5: Set the wax ring {#step-5-wax-ring}

There are two schools of thought, and they both work:

Option A, wax ring on the flange: Unwrap the wax ring and press it firmly down onto the flange, centered over the drain. The plastic horn (if your ring has one) points down into the pipe.

Option B, wax ring on the bowl: Flip the bowl upside down on a towel, press the wax ring onto the bottom of the bowl horn, then carry it to the flange.

I prefer Option A because the wax stays where I put it. Option B is fine if you have a helper.

Either way, do this only once. Wax does not survive being pressed and lifted. If you set the bowl wrong and lift it back up, scrape the wax off and use a new ring. They’re $4. Don’t try to reuse one.

Waxless alternatives: Korky NeverLeak, Fluidmaster Better Than Wax, and similar rubber/foam gaskets are more forgiving. They allow a bowl to be lifted and reset without ruining the seal, and they don’t degrade over time the way wax can. They cost about $10 instead of $4. For a first install, they’re worth the upcharge.

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Step 6: Lower the bowl and seat the wax ring {#step-6-set-bowl}

This is the moment that goes wrong most often. The bowl weighs 50 to 60 pounds on its own (the tank is the other 30 to 40). You’re going to lower it straight down onto two bolts you can’t see, into a wax ring that grabs the bowl on contact.

1. Pull the rag out of the drain pipe. Last chance.
2. Lift the bowl by the rim, not the holes in the base.
3. Position yourself with the bowl directly over the bolts. Eyeball both bolt locations through the two holes in the bowl base. Get a helper to call out left/right if you have one.
4. Lower straight down until the bolts come up through the holes and the bowl rests on the wax ring.
5. Press down with your full weight, evenly, while gently rocking front-to-back and side-to-side. You’ll feel the bowl drop another quarter to half inch as the wax compresses. Stop when the bowl is sitting flat on the floor (or on the flange, if it’s slightly raised).

Do not stand on the bowl. Sit on it, with your weight centered. Standing on the rim is how brand-new toilets crack.

Check level in two directions with a small torpedo level. If it’s off, shim with plastic toilet shims (never wood, they rot) between the bowl and the floor before tightening the bolts.

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Step 7: Tighten the closet bolts slowly and evenly {#step-7-tighten-bolts}

This step cracks more toilets than any other. Snug is the target. Crushed is the failure mode.

1. Slip the brass washer onto each bolt.
2. Thread the nut down by hand until it’s finger-tight.
3. With a wrench, turn each nut a quarter-turn at a time, alternating sides. Left, right, left, right. Never crank one side all the way down before starting the other.
4. Stop when the bowl feels firmly seated and won’t rock. The bolts should be tight, not white-knuckle tight. If you have to lean into the wrench, you’re past the right point.
5. Try to rock the bowl gently. It shouldn’t move. If it does, give each side another quarter-turn.

Porcelain cracks around the bolt holes when overtightened. Sometimes the crack is invisible for a week, and then the toilet splits when someone sits on it. Snug, not crushing.

Once the bowl is secure, cut the closet bolts with a small hacksaw so they sit about a quarter-inch above the nut. Press the plastic caps over the bolt heads. They’ll snap into place. On some brands, fill them with a dab of clear silicone first to keep them from popping off when cleaned around.

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Step 8: Install the tank (two-piece toilets only) {#step-8-tank}

For a one-piece toilet, skip this step. For a two-piece (the more common DIY install) the tank goes on after the bowl is bolted down.

1. Check the tank-to-bowl gasket (the thick rubber donut on the bottom of the tank). New toilets come with it pre-installed; verify it’s seated.
2. Lift the tank, align the tank bolts with the two holes in the bowl, and lower it straight down. The gasket will compress slightly.
3. Slip rubber washers, then metal washers, then nuts onto the bolts from underneath. Hand-tight first.
4. Tighten with a screwdriver in the bolt head (from inside the tank) and a wrench on the nut underneath. Quarter-turn at a time, alternating sides, exactly like the closet bolts.
5. Stop when the tank is firm against the bowl. Slight side-to-side wiggle is okay. The rubber gasket does the sealing, not the metal-on-porcelain pressure.

Overtightening here is what cracks tanks. Same rule: snug, not crushing.

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Step 9: Reconnect the supply line {#step-9-supply}

1. Hand-thread the new braided supply line onto the shut-off valve and onto the tank ballcock. Most fail-points happen because someone cross-threaded a nut on the first half-turn.
2. Snug each end with a wrench. About a quarter-turn past hand-tight. Braided supply lines use rubber washers; they seal under modest pressure. Cranking down on them deforms the washer and causes leaks.
3. Check that the supply line has a gentle curve, not a kink. Kinks fail. Choose a longer line if needed.

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Step 10: Turn the water on and fill the tank {#step-10-fill-tank}

Turn the shut-off valve counterclockwise, slowly. Watch for spray. Listen for the tank filling.

While it fills, watch the supply line connection at both ends, the bolts at the base of the tank, and the inside of the tank itself for any drips.

When the fill valve shuts off, flush once. The bowl will fill, the tank will refill, and you’ll learn whether everything is sealed.

Flush a second time and watch the base of the bowl for any seepage onto the floor. Press a folded paper towel against the floor around the base. If it stays dry, the wax ring is sealed.

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Step 11: Check for leaks (the careful 10-minute version) {#step-11-leak-check}

A toilet that doesn’t leak at minute 5 can still leak at minute 30. Do the following, in order:

1. Wipe the floor around the base dry. Tear a paper towel into four strips and lay them on the floor in a ring around the base.
2. Flush three times in a row, with about a minute between each flush.
3. Press a dry paper towel against the tank-to-bowl seal, the supply line connections, and the base. Look for any moisture.
4. Come back in 30 minutes. Check the paper towels on the floor. Run a fingertip along the underside of the tank where it meets the bowl.

A slow leak at the wax ring shows up here. Not immediately, but within an hour. If you see any moisture at the base, the bowl wasn’t seated fully, or the wax ring didn’t compress evenly. The fix is to lift the bowl and use a new ring. Annoying, but doing it now is far cheaper than discovering it through a stained ceiling downstairs.

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Step 12: Caulk the base, when and when not to {#step-12-caulk}

This one’s debated by plumbers, and both sides have reasonable arguments.

Caulk the base if:

• Local code requires it (many do; IRC P2705.1 in some jurisdictions)
• The floor is uneven and you can see daylight under the bowl
• The bathroom is shared with a shower or tub that can splash water around the base
• You want to prevent mop water and dust from getting trapped under the bowl

Skip caulk if:

• You want any future base leak to drip out where you can see it instead of pooling under the toilet and rotting the subfloor

The compromise (what most pros do) is to caulk the front and sides of the base but leave a 2- to 3-inch gap at the back, hidden by the wall. Any future leak escapes there as a visible drip instead of soaking the subfloor.

Use 100% silicone caulk (not “siliconized acrylic” or “tub and tile”). Run a thin bead around the base, then smooth it with a wet fingertip. Wipe excess immediately. Silicone is a nightmare once cured.

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Step 13: Install the seat {#step-13-seat}

The seat almost always ships separately. Two plastic bolts drop through the holes at the back of the bowl, with plastic nuts that thread on from underneath. Hand-tight only. Plastic on porcelain cracks porcelain the same way brass does.

Most modern seats have a quick-release feature for cleaning. Line up the markings on the seat hinges before snapping them shut.

That’s it. Wash up and check for any leaks tomorrow morning.

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Common problems and how to fix them {#common-problems}

The bowl rocks. The floor isn’t level, or the closet bolts weren’t tightened evenly. Loosen both bolts, slide plastic toilet shims under the bowl where there’s a gap, then re-tighten alternating sides. Trim the shims flush with a utility knife and caulk over them.

Water seeps out around the base after a flush. The wax ring didn’t seal. Lift the bowl, scrape off the old wax, install a new ring (consider going extra-thick or switching to a waxless gasket), and re-set.

The toilet runs constantly. Almost always the fill valve or the flapper, not the install. Adjust the float height in the tank. If a Fluidmaster or Korky fill valve is hissing, the diaphragm has failed. A $10 replacement, 10-minute job.

The supply line drips at the tank end. The rubber washer inside the nut wasn’t seated, or the nut is overtightened. Turn the water off, disconnect, check the washer, hand-tighten the nut plus a quarter-turn.

A small puddle appears under the tank on the bowl after a flush. The tank-to-bowl gasket isn’t seated. Drain the tank, lift it off, check the rubber gasket for proper position, and reset. This is also a common spot for condensation on the tank in humid bathrooms. Wipe and see if it returns.

The closet bolts won’t tighten; they just spin. The brass bolts have spun loose in the flange slot. Hold the bolt head with pliers while you turn the nut. If the slot is broken, the bolts can’t anchor. You need a repair ring under the flange.

Sewer smell after install. Either the wax ring didn’t seal (see above), or the toilet wasn’t set with the bowl horn properly into the wax. Lift and reset.

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When to call a plumber {#when-to-call-a-plumber}

Stop and call a plumber if any of these show up:

• The flange is broken below the floor level. Repair rings work above the floor; below, the cast iron or PVC pipe itself may need to be cut and replaced.
• The subfloor is soft, spongy, or stained dark around the flange. Water damage means rot, and rot means structural repair before the new toilet goes down. A new toilet on a rotten floor will fail within a year.
• There’s a lead bend (a flexible gray-silver pipe between the flange and the cast iron stack, common in homes built before 1960). Lead bends require special wipe joints and shouldn’t be DIY’d.
• You see asbestos floor tile. Small (usually 9″x9″), often brittle, common in homes built between 1920 and 1980. Disturbing it releases fibers. Test before disturbing.
• The shut-off valve fails and you can’t get it to close. You’ll need to replace it, which involves draining a section of the house’s plumbing.
• You smell sewer gas through the floor even with the toilet bagged and the drain rag in place: that means a vent or sewer line problem that’s beyond a toilet install.
• The drain pipe coming up through the floor is cast iron and visibly corroded at the flange. Cast iron pipes from the mid-century era are reaching end of life; a plumber should evaluate.

A plumber typically charges $200 to $400 for a toilet install if you supply the toilet. Add $100 to $300 if they’re hauling the old one. For straightforward swaps it’s not a great use of money, but for any of the above scenarios it’s the cheap option.

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FAQ {#faq}

Can I install a toilet myself?

Yes, in almost all cases. A toilet swap into an existing flange is one of the more approachable plumbing DIY projects: no sweating copper, no shutting off the house main, no permit in most jurisdictions. The two things that make it harder than it looks: the toilet is heavy and awkward, and the wax ring is unforgiving of a sloppy set. If you can lift 60 pounds and follow instructions carefully, you can do this.

How long does it take to install a toilet?

Plan on 60 to 90 minutes for a swap into a clean, existing flange. Add 30 minutes if it’s your first install. Add a couple of hours if you have to deal with a corroded shut-off valve, stuck old bolts, or a flange repair. Demolition-and-install of a damaged old setup can run a full afternoon.

Do I need to caulk the base of the toilet?

Local code in many areas requires it. Check IRC P2705.1 and your municipal amendments. Beyond code, caulking keeps mop water and dust out from under the bowl and reduces movement. The widely used compromise is to caulk the front and sides but leave a 2- to 3-inch gap at the back, so any future leak can escape and warn you instead of rotting the subfloor invisibly.

What if my floor isn’t level?

Most floors aren’t perfectly level. That’s normal. Set the bowl, check with a small torpedo level in two directions, and slide plastic toilet shims under the low side until the bowl is level and stable. Tighten the bolts evenly, trim the shims flush with a utility knife, and caulk over them. Never use wood shims; they rot.

Why does my new toilet rock?

Three possibilities, in order of likelihood: the bolts weren’t tightened evenly (alternate quarter-turns side to side); the floor isn’t level and the bowl needs shimming; or the wax ring wasn’t compressed fully when the bowl was set. A rocking toilet will break the wax seal within weeks. Fix it now.

How tight should toilet bolts be?

Snug, not crushing. The bolts should hold the bowl firmly against the floor with no rocking, but you should not be leaning into the wrench. Overtightened bolts crack porcelain, sometimes immediately, sometimes weeks later when someone sits down. Alternate quarter-turns side to side and stop the moment the bowl is solid.

Why is my new toilet leaking at the base?

Almost always a wax ring that didn’t seat properly. Causes: the bowl was lifted and reset after the wax first touched (wax doesn’t reseal); the flange sits below the finished floor and a standard ring couldn’t reach; or the bowl was lowered crooked. Fix: lift the bowl, scrape off all the old wax, and set a new ring. Waxless gaskets like Korky NeverLeak are more forgiving on the second attempt.

Can I reuse the old wax ring?

No. Wax compresses when first installed and loses its ability to form a seal once disturbed. A new ring costs $4 to $10. That’s the cheapest insurance you’ll buy that day. Reusing the old ring is the most common cause of base leaks after a DIY install.

Do I need a permit to replace a toilet?

In most US jurisdictions, no. Replacing an existing fixture in the same location doesn’t require a permit. New installations during a remodel often do. Check your local building department before starting a bathroom renovation, but a straight swap is almost always permit-free.

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Written by Ariel, who has installed seven toilets across five houses, cracked exactly one tank with an overtightened bolt (lesson learned), and now keeps a spare wax ring in the garage at all times. Last updated May 28, 2026.

Sources & references

• IAPMO: Uniform Plumbing Code rough-in standards
• Fluidmaster: wax ring vs. waxless seals