Toilet supply line guide: sizes, lengths, line types, and the ones that fail
Toilet supply line guide: sizes, lengths, line types, and the ones that fail
By Ariel, last updated September 25, 2026.
A toilet supply line is the short pressurized hose between the shutoff valve at the wall and the fill valve under the tank. It is the only part of a toilet under house pressure around the clock, which is how a five-dollar part ends up behind so many ruined ceilings. This guide covers line types, thread sizes, lengths, what the code asks for, and the lines we would put on our own toilets.
The toilet supply line to buy
Buy a braided stainless line, 3/8 inch compression at the stop and 7/8 inch ballcock at the tank. Our default is the Fluidmaster B1T12CS Click Seal, 12 inch, $3.90 observed at SupplyHouse in September 2026; check current pricing at Lowe’s. For a metal tank nut, the BrassCraft Speedi Plumb PLUS B1-12DLM F was $9.49 observed at HD Supply in September 2026.
Tighten by hand plus a quarter turn, no tape, no putty. If the stop is a multi-turn valve that weeps or will not close, replace it with a quarter-turn stop while the water is off; the BrassCraft G2CR19X C was $8.43 observed at SupplyHouse in September 2026.
Toilet supply line types at a glance
| Line type | Where it fails | Verdict |
|---|---|---|
| Braided stainless, PVC core | Ferrule corrodes; plastic nut cracks under a wrench | Default; installers commonly replace at 5-10 years |
| Braided polymer, PVC core | Jacket scuffs; same nut issues | Good where cleaners or salt air eat stainless |
| Plain vinyl | Splits along its length | Do not buy |
| Rigid chrome copper or brass | Kinks if bent twice; leaks if misaligned | Exposed tanks only |
Prices for the braided lines and the stop are in the picks below.
What a toilet water supply line actually is
Five things in a row: the stop valve, its 3/8 inch compression outlet, the line’s compression nut squeezing a brass sleeve or molded cone against that outlet, the line, and the 7/8 inch ballcock nut sealing a rubber washer against the end of the fill valve shank, which is the tank inlet. Nothing in that chain seals on its threads, which is why tape only holds the nut off its seat and a wrench past snug crushes the washer.
The four line types and where each one fails
Braided stainless over a PVC core is what every maker sells as no-burst. The core seals; the braid keeps it from ballooning. Fluidmaster rates its Click Seal line to 1500 psi burst (Fluidmaster Click Seal FAQ), which leaves the crimp and the nut as the weak points.
Braided polymer swaps the steel for a polymer-coated fiber braid. BrassCraft’s Speedi Plumb PLUS is the common one, rated 125 psi and 40 to 160 degrees F (BrassCraft product page). Nothing in the jacket rusts; it scuffs where it rubs tile.
Plain vinyl has no jacket. It hardens, splits lengthwise, and full house pressure comes out of the slit.
Rigid chrome-plated copper or brass suits an exposed tank. It bends once and lasts as long as nobody touches it; a second bend kinks it.
Old flexible copper risers with an acorn head work-harden every time the tank is moved and crack at the nut. Green on the nut is the tell.
Toilet supply line size: the two threads, and the odd ones
The standard is 3/8 inch compression at the stop and 7/8 inch ballcock at the tank. The 7/8 inch thread is universal on modern fill valves, so a line that fits a Fluidmaster 400A fits a Korky, a Kohler, or a TOTO shank. The odd cases:
- A 1/2 inch compression outlet, where 1/2 inch copper runs straight into the stop. Eastman lists 7/8 by 1/2 inch compression lines in 9, 12, and 16 inches (48092, 48114, 48094) on its Steel-Flex page.
- A 1/2 inch FIP outlet on an old iron-pipe stop. Buy a line labeled 1/2 inch FIP; forcing a 3/8 compression nut on strips the stop.
- A 7/16 inch compression outlet on some older stops. Eastman’s 48739 (12 inch) and 48741 (20 inch) are the current toilet lines in that size.
Lengths: 9, 12, 16, 20 inches, and how to measure
BrassCraft lists 6 to 20 inches, Eastman 9 to 20, and Fluidmaster’s Click Seal 12 to 20. In most homes a 12 inch line reaches from a wall stub to the shank. Nine is for a high stop; sixteen and twenty are for floor stubs, offset stops, and tall or skirted tanks. Measure from the stop outlet to the end of the shank along the path the hose will follow and add two inches for a relaxed curve. Never pull a flex line straight. Between sizes, buy the longer one.
Why a no-burst line still fails
The burst rating describes the tube. Lines fail elsewhere. The crimp, where the braid is swaged onto the brass insert under the nut, is where installers report chloride attacking the stainless first: cleaners, bleach tablets in the tank, coastal air. A rust-brown bloom at the ferrule is the warning. The nut fails two ways: a plastic ballcock nut cracks under a wrench (Fluidmaster rates its Click Seal nut at 15 to 20 inch-pounds, a firm hand and nothing more), and a brass nut cross-threads on the plastic shank when started crooked. A line forced into a run too long for it kinks behind the nut. And a reused line drips because its washers took a set, which is why our installing a new toilet guide says buy new every time.
Installing it: hand-tight plus a quarter turn, then the water-off checklist
Run both nuts down by hand. Add a quarter turn with a wrench on the metal compression nut at the stop; Fluidmaster’s sheet directs a half turn and says to tighten only enough to stop a leak; Roto-Rooter says never more than a quarter (Roto-Rooter, changing a toilet supply line). We do a quarter and add an eighth only if it weeps. The plastic ballcock nut gets hand pressure only.
Replace the stop too if it is multi-turn and weeps at the stem, will not close fully, or has a green stem: on copper, a compression swap with the house main off; on PEX or CPVC, the stop made for that pipe.
The water-off checklist:
- Find the house main first, in case the stop will not close.
- Close the stop, flush, hold the lever, sponge out the last inch.
- Towel and pan down; disconnect the tank end first, then the stop end.
- A scored, out-of-round, or green stop stub means a new sleeve or stop.
- Tank nut by hand; stop nut by hand plus a quarter turn. Open the stop slowly, watch both nuts for a minute, check again after the tank fills and the next morning, then date the braid.
An adjustable wrench, towel, pan, and flashlight cover it; the plumbing tools for homeowners list has the push-to-connect stop and the close-quarters tubing cutter that turn a stop swap into a job without a torch.
What the plumbing code asks of a toilet supply line
In Chapter 6 of the 2021 International Plumbing Code, Section 604, Design of Building Water Distribution System, includes 604.5, Size of Fixture Supply: Table 604.5 sets a 3/8 inch minimum fixture supply for a flush-tank water closet and 1/2 inch for a one-piece toilet (that table covers the pipe in the wall), the supply pipe terminates within 30 inches of the fixture, and a reduced-size flexible connector “shall be of an approved type.” Section 605, Materials, Joints and Connections, includes 605.6: flexible water connectors under continuous pressure conform to ASME A112.18.6/CSA B125.6, and access shall be provided (IPC 2021, Chapter 6, codes.iccsafe.org). Look for that standard on the package, and leave the connection reachable.
The 2021 Uniform Plumbing Code covers the same ground in Section 604.5, Flexible Connectors, and Table 610.3 (2021 UPC table of contents, IAPMO).
The insurance angle
The Insurance Institute for Business & Home Safety’s study of thousands of interior water damage claims lists plumbing supply system failure first among five leading sources and toilet failure second. Allstate’s summary of that study (2012) says IBHS found one-third of toilet failures came from overflows or clogs, and its advice is to inspect the fill valve, flush valve, and supply line twice a year and replace as needed (Allstate, suggestions to reduce water damage). Travelers tells policyholders to include “supply lines, hoses, connections and fittings” in an annual inspection (Travelers, how to help prevent water damage). Close the stop when the house will sit empty for more than a few days, and treat the date on the braid as a replacement date.
The picks: three supply lines and one stop we would install
The picks are based on manufacturer specs and installer feedback, with prices observed at named retailers in September 2026.
1. Fluidmaster B1T12CS Click Seal, 12 inch: best overall
What it does well:
- 1500 psi burst rating, and the tank nut ratchets with a click at the right torque and will not go tighter.
- NSF/ANSI 61, UPC, and CSA listed, 5-year limited warranty (Fluidmaster store listing, Fluidmaster warranty details).
What you give up:
- The ratchet clicks in the tightening direction only, which confuses people on removal, and a weeping nut on a scratched shank cannot be snugged.
- The plastic ballcock nut takes hand pressure only; a wrench cracks it.
Spec: 12 inch, 3/8 inch compression by 7/8 inch ballcock. $3.90 for the 12 inch observed at SupplyHouse and $11.99 to $13.99 for the 16 and 20 inch at Fluidmaster’s store in September 2026; check current pricing at Lowe’s (SupplyHouse, Lowe’s, Fluidmaster direct).
2. BrassCraft Speedi Plumb PLUS B1-12DLM F, 12 inch: best with a metal tank nut
What it does well:
- Braided polymer over PVC tubing, nothing in the jacket to corrode at the crimp; rated 125 psi and 40 to 160 degrees F; 6 to 20 inch lengths.
- Metal ballcock nut; the B1-12DL F is the same line with a hand-tighten wing nut (BrassCraft, metal nut and wing nut).
What you give up:
- A metal nut strips a plastic shank if you go past hand-tight plus a quarter turn, and the jacket scuffs on tile.
Spec: 12 inch, 3/8 inch compression by 7/8 inch ballcock, metal tank nut. $9.49 observed at HD Supply in September 2026 (HD Supply listing).
3. Eastman Steel-Flex 48088, 12 inch: best for odd stop sizes
What it does well:
- PVC core, nylon reinforcement, grade 304 stainless braid, chrome-plated solid brass ballcock nut; UPC listed, NSF and CSA certified, lead-free (Eastman Steel-Flex).
- The 3/8 inch family runs 9, 12, 16, and 20 inches (48087, 48088, 48089, 48090).
What you give up:
- A brass nut on a plastic shank cross-threads if started crooked, with no click to stop you.
- Not in the big-box aisle, so it is an order rather than a Saturday pickup.
Spec: 12 inch, 3/8 inch compression by 7/8 inch ballcock, chrome-plated brass tank nut. $5.79 observed at Zoro in September 2026 (Zoro listing).
4. BrassCraft G2CR19X C quarter-turn angle stop: the stop to replace a multi-turn
What it does well:
- Fits the most common wall stub, 1/2 inch nominal copper, with a 3/8 inch compression outlet; one-piece brass body, chrome plated, factory leak-tested, lead-free (BrassCraft G2 angle stop).
What you give up:
- A scarred or out-of-round stub needs a new sleeve, maybe a stub repair, before it seals.
- Made for copper stubs; PEX, CPVC, and iron pipe need the stop BrassCraft makes for that pipe.
Spec: 1/2 inch nominal compression inlet by 3/8 inch compression outlet, quarter turn. $8.43 each observed at SupplyHouse in September 2026, $7.99 each in a box of five (SupplyHouse listing).
What you need before buying a supply hose for the toilet
Four measurements and one look: the stop outlet size (3/8 inch compression on most modern stops; 1/2 inch, 1/2 inch FIP, or 7/16 inch on the odd ones), the tank inlet (7/8 inch ballcock on every modern fill valve), the length along the hose path plus two inches, and the pipe the stop is on. The look: a multi-turn stop gets replaced. Budget $4 to $12 for a braided line and $8 to $9 for a quarter-turn stop, observed at SupplyHouse, HD Supply, and Zoro in September 2026. An old fill valve gets swapped now too; see the fill valve replacement guide.
What this article will not recommend
Plain vinyl lines, at any price. Reusing the old line on a new toilet or fill valve; the washers have taken a set. Tape or dope on either nut, which holds the nut off its seat.
Combined push-fit stop-and-hose kits as a default. Handy on a bare stub, but when the hose fails you replace the valve with it. If you want one, the current number is the SharkBite UR24656, which replaced the 24656; it was $19.05 observed at SupplyHouse in September 2026; check current pricing at Lowe’s (SupplyHouse, Lowe’s). A separate stop and line cost less and replace independently.
Toilet drain: what happens after the tank
The drain side has no pressure and no moving parts. Tank water enters the bowl through the rim jets, fills the trapway cast into the base, and once the trapway runs full it siphons the bowl empty. The bowl’s outlet sits on a wax ring or rubber gasket sealed to the closet flange, and a closet bend under the flange turns the 3 or 4 inch drain line toward the stack. Clogs live in the trapway; leaks and smells at the floor live at the wax ring. The parts of a toilet glossary walks the path and the wax ring guide covers the seal. What goes down that trapway matters as much as the seal under it; our what can you flush guide covers the items that snag in it.
FAQ
What size is a standard toilet supply line?
3/8 inch compression at the stop and 7/8 inch ballcock at the tank, in 9, 12, 16, or 20 inch lengths. The odd stop sizes are 1/2 inch compression, 1/2 inch FIP, and 7/16 inch.
Are toilet supply lines universal?
The tank end is; every modern fill valve takes a 7/8 inch ballcock nut. Check the stop outlet, and do not buy a faucet line, whose 1/2 inch FIP end will not fit a toilet shank.
How tight should the supply line nuts be?
Hand-tight, then a quarter turn with a wrench on the metal compression nut at the stop. The plastic ballcock nut gets hand pressure only. No tape, dope, or putty on either end.
How often should I replace a toilet supply line?
No code sets an interval; installers commonly replace a braided line at 5 to 10 years (Fluidmaster warrants the Click Seal for 5), sooner if you see rust at the crimp, a cracked nut, a kink behind the nut, or green on the threads. Replace it any time it comes off.
Can I use Teflon tape on a toilet supply line?
Not on the compression nut or the ballcock nut; both seal on a sleeve or a washer, and tape keeps the nut from seating. Tape belongs only on a 1/2 inch FIP connection at an old iron-pipe stop.
Why is my new supply line leaking at the tank?
Usually a wrenched plastic nut that cracked, a nut started crooked and cross-threaded, or tape on the threads holding the nut off the washer. Take it off, check the washer and the shank end, and reinstall by hand.
Does the toilet chain have anything to do with the supply line?
No. The toilet chain is inside the tank on the flush side, and it wants about half an inch of slack when the flapper is seated, the one to two loose links Korky’s instructions call for (Korky, how to replace a toilet flapper). Too tight and the flapper cannot seat, so the toilet runs. Too loose and it pools under the flapper and holds it open, which is the phantom flush. Sizing the flapper is in the flapper replacement guide.
Sources & references
- ICC, 2021 International Plumbing Code, Chapter 6
- IAPMO, 2021 Uniform Plumbing Code table of contents and IAPMO
- Fluidmaster, Click Seal toilet supply line, Click Seal instructions and FAQ, Click Seal store listing and warranty details
- BrassCraft, Speedi Plumb PLUS toilet connector, Speedi Plumb PLUS with metal nut and G2 quarter-turn angle stop
- Eastman, Steel-Flex compression braided toilet connector
- Allstate, suggestions to reduce water damage
- Travelers, how to help prevent water damage
- Korky, how to replace a toilet flapper
- Roto-Rooter, how to change a toilet’s water supply line
