How often should you replace a toilet supply line?

Replace a braided stainless-steel supply line about every 5 to 8 years, and replace any rubber or plastic line on sight — those harden, crack and are a leading cause of quiet, catastrophic bathroom flooding. There is no strict expiry, but a supply line is a few dollars and holds constant house pressure, so proactively swapping an old one is cheap insurance. Replace it immediately if you see corrosion at the connections, a bulge or kink in the line, mineral crust, or any dampness where it connects.

What size supply line does a toilet need?

A toilet supply line has a 7/8-inch ballcock nut on the tank end (a wide, thin-walled coupling that fits the fill-valve shank) and a 3/8-inch compression nut on the shut-off valve end, which is the common US size. Buy a line labeled for a toilet so you get the correct 7/8-inch tank connector — a faucet line with two 3/8-inch ends will not fit the tank. For length, measure from the shut-off valve to the tank inlet and add a couple of inches of slack so the line is not stretched taut.

Why is my toilet supply line leaking at the connection?

Usually an over- or under-tightened nut, a missing or pinched rubber washer, or a cross-threaded connection. Braided lines seal on a rubber gasket inside the nut — hand-tighten firmly, then only a quarter turn more with a wrench. Cranking the thin plastic ballcock nut on the tank end is the classic error: it cracks or deforms and leaks worse. Confirm the washer is seated, thread the nut on straight by hand first to avoid cross-threading, and do not overtighten. The tank-end nut is meant to be hand-snug.

Can I replace a toilet supply line without turning off the water?

You should always turn it off first. Close the shut-off valve behind the toilet, flush and hold the handle to drain the tank, and sponge out the last of the water before disconnecting the line. The line is under constant pressure, so removing it with the valve open sprays water everywhere. If the shut-off valve itself will not fully close or weeps, that is a separate repair — replace the valve — but for a routine supply-line swap the fixture shut-off is all you need to close.

Should I use a braided steel or plastic toilet supply line?

Braided stainless steel, without question. Braided lines have a flexible inner tube protected by a woven stainless sleeve that resists bursting and is far more durable than bare plastic or rubber lines, which harden and split with age. They cost only a dollar or two more and are the standard recommendation for any water-supply connection you want to forget about. Reserve rigid chrome or plastic lines for situations that specifically call for them; for a toilet, braided stainless is the safe default.

How to Replace a Toilet Supply Line: 15-Minute Fix

Written & researched by Priya Anand DIY & Tools Editor

Updated August 2026

Low-angle view of a person's hands tightening a fitting under a kitchen sink with a wrench, in soft overcast light

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Replacing a toilet supply line is one of the quickest plumbing jobs — about 15 minutes, a few dollars for a braided stainless line, no permit and no plumber. If the line is old, corroded, plastic, or weeping, swap it. You shut off the water, drain the tank, disconnect the old line, and connect a new braided line hand-tight plus a quarter turn. The only real error is over-tightening the thin tank-end nut and cracking it. A supply line holds constant house pressure, so a fresh braided one is cheap protection against a flood.

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How to Replace a Toilet Supply Line — Easy DIY Plumbing Guide

Tools and materials

A new braided stainless-steel toilet supply line (7/8-inch tank end, 3/8-inch valve end) of the right length.
An adjustable wrench, a sponge and bucket, and a towel.
Basic hand tools — see best plumbing tools.

Close-up detail of the material being worked in a diy plumbing project, in soft overcast light

Step 1: Buy the right line

Measure from the shut-off valve up to the tank inlet and add two inches of slack, so the line curves gently rather than pulling taut. Buy a line labeled for a toilet to get the wide 7/8-inch ballcock nut on the tank end and the 3/8-inch compression nut for the valve. A faucet line will not fit the tank.

Step 2: Shut off and drain the tank

Close the shut-off valve behind the toilet (clockwise) and flush, holding the handle to empty the tank. Sponge out the remaining water so nothing spills when you disconnect the line. Keep a towel and bucket under the connections.

Three-quarter view of a person's hands tightening a fitting under a kitchen sink with a wrench, in soft early-morning light

Step 3: Disconnect the old line

Unscrew the nut at the tank end (the wide 7/8-inch nut on the underside of the tank) and the nut at the shut-off valve. Hold the valve body steady with a second wrench so you do not twist it. Remove the old line and let any water drain into the bucket.

Step 4: Connect the new line

Thread the tank end (7/8-inch nut) onto the fill-valve shank by hand — this thin plastic nut is meant to be hand-snug, so do not put a wrench on it hard. Thread the valve end (3/8-inch nut) onto the shut-off by hand, then a quarter turn with the wrench. Confirm the rubber washers are seated and that neither nut is cross-threaded. Let the line curve gently, not kinked or stretched.

Golden-hour view of a person's hands tightening a fitting under a kitchen sink with a wrench

Step 5: Turn on the water and test

Open the shut-off valve slowly and let the tank fill. Feel both connections with a dry finger and watch for any bead of water. Flush once. Check again after a few minutes under pressure. A weep at the tank end usually means the nut needs to be hand-snugged a touch more or the washer re-seated — not wrenched hard.

Common mistakes

Over-tightening the plastic tank-end nut, cracking it — hand-tight is correct.
Buying a faucet line that lacks the 7/8-inch tank connector.
A line too short and pulled taut, which stresses the connections.
Reusing an old rubber or plastic line instead of upgrading to braided stainless.

When to call a plumber

This is DIY for everyone, with no permit. The only escalation is if the shut-off valve behind the toilet will not close or weeps at the stem — then replace the valve (see how to replace a water shut-off valve), and if that valve is soldered or on old galvanized pipe, a plumber handles it. A leaking supply line that has already caused soft or discolored flooring may hide subfloor damage worth having assessed.

How to Replace a Toilet Supply Line