How to Replace a Toilet Supply Line

What a toilet supply line does

A toilet supply line carries water from the shut-off valve on the wall or floor to the fill valve on the bottom of the toilet tank. Most modern toilets use a flexible braided stainless steel line with a nut at each end. One end connects to the shut-off valve, usually a 3/8 inch compression fitting, and the other connects to the fill valve shank at the base of the tank.

Replacing a supply line is one of the most straightforward plumbing repairs in a bathroom. You do not need to remove the toilet or work with the wax ring, flange, or any part of the bowl. The line is accessible from the outside of the toilet, so the job is quick even for a first-time homeowner.

For more on the components that make up a toilet, see our guide to toilet parts and learn how each piece connects.

Signs the supply line needs replacement

A supply line should be replaced when you see cracks, bulges, or corrosion on the braided exterior, when the nuts are rusted or stripped, or when there is any moisture at the connections. Leaks at the supply line are a common cause of bathroom water damage, and the EPA notes that household leaks can waste a significant amount of water each week.

Most flexible supply lines have a manufacturer-recommended lifespan, but the more practical rule is to replace the line whenever you service the toilet or notice any sign of wear. If the shut-off valve is old and hard to turn, plan to replace it while you have the water off. See our guide on installing a toilet shut-off valve for that process.

If you are replacing the fill valve or the flapper at the same time, a new supply line is a small addition to the project. Our guide to replacing a toilet fill valve covers that part of the job.

Tools and materials you will need

The tool list is short. You need an adjustable wrench, a bucket or towel, and a new supply line. A pair of pliers can help if the nuts are stuck, but an adjustable wrench is usually enough. A flashlight helps you see the connection at the base of the tank.

Before you buy a replacement line, measure the distance from the shut-off valve to the fill valve connection. Supply lines come in standard lengths, so choose one that reaches without pulling tight. A line that is too short puts strain on the fittings, and one that is too long can kink.

For information on sizing a supply line correctly, see our article on toilet supply line size.

• Adjustable wrench
• New braided stainless steel supply line
• Bucket or towels
• Flashlight (optional)
• Teflon tape (optional, for threads)

Step-by-step replacement guide

The steps below are for a standard flexible supply line with a nut at each end. The process for a rigid chrome line is similar, but a flexible line is easier to install and less likely to leak, which is why it is the common choice for modern toilets.

Step 1: Turn off the water. Locate the shut-off valve behind or beside the toilet and turn it clockwise until it stops. If the valve is old and does not turn easily, apply gentle pressure and stop if you feel resistance. A broken valve is a bigger problem than a leaking supply line.

Step 2: Drain the tank. Flush the toilet and hold the handle down to let as much water as possible run out. Use a bucket or towel to soak up the remaining water at the base of the tank.

Step 3: Disconnect the old line. Place a bucket under the connection at the tank and loosen the nut with your adjustable wrench. Turn counterclockwise. Once the tank end is loose, loosen the nut at the shut-off valve the same way. Pull the old line free.

Step 4: Inspect the threads. Look at the threads on the shut-off valve and the fill valve shank. They should be clean and free of corrosion. A small amount of Teflon tape wrapped clockwise around the threads can help ensure a good seal, though many new lines have a rubber gasket that makes tape unnecessary.

Step 5: Attach the new line. Thread the nut onto the fill valve shank by hand, turning clockwise until it is snug. Do not cross-thread the nut. Then connect the other end to the shut-off valve the same way. Tighten both nuts with the wrench, but do not over-tighten. The nuts should be snug plus about a quarter turn.

Step 6: Turn the water back on. Open the shut-off valve slowly, counterclockwise. Watch the connections for leaks. Let the tank fill, then flush the toilet and check again. If you see a drip, tighten the nut slightly.

For a guide to detecting leaks after the replacement, see how to test for toilet leaks.

Common mistakes and how to avoid them

The most common mistake is cross-threading the nut at the fill valve. The nut should thread on smoothly by hand. If you need force to start it, stop and re-align the nut.

Another mistake is choosing a line that is too short and pulling it tight to make the connection. This puts constant stress on the fittings and can cause a leak months later. Pick a length that reaches with slack.

A third mistake is turning the water back on too quickly. Open the valve slowly so the sudden pressure does not shock the connections. A slow opening also gives you time to spot a leak before it sprays.

If your shut-off valve is old, the handle may be stuck. Do not force it with pliers, as this can break the valve stem. Replace the valve as part of this project. See how to install a toilet shut-off valve.

Safety tips

Work in a well-lit area. Use a flashlight if the connection at the tank is in shadow, especially on a two-piece toilet where the supply line enters the bottom of the tank.

Do not use a wrench on the shut-off valve handle to force it if it is stuck. A broken valve can cause water to spray. If the valve fails, shut off the water at the main house valve before continuing.

Hold the tank nut with one hand while you tighten the supply line nut with the other. The fill valve shank can spin if you do not support it, which may loosen the nut that holds the fill valve to the tank.

CPSC safety education emphasizes the importance of addressing potential hazards promptly around the home. A slow leak under a toilet can damage flooring over time, so check the connections a day after the install as well.

If you are working on a toilet in a children's bathroom, remember that a secure connection is essential to avoid injury from hot water or slips. See our guide to choosing toilets for children for related considerations.

When to call a professional

Most homeowners can replace a supply line without help, but there are situations where a plumber is the safer choice. If the shut-off valve is corroded to the point that it will not close, if the pipe behind the valve is damaged, or if you cannot stop a leak after tightening, call a professional.

If your toilet is a wall-hung model, the supply connection may be inside the wall or behind an access panel. See our guide to wall-hung toilet requirements for details on that type of installation.

A macerating toilet has a pump unit that includes additional plumbing connections. If you are unsure whether the supply line connects differently on your unit, see what is a macerating toilet before starting.

What to pick for your replacement

Questions

How long does it take to replace a toilet supply line?

About 15 to 30 minutes, including draining the tank and checking for leaks. No special skills are needed.

Do I need Teflon tape on the new supply line?

Most new braided lines have a rubber gasket inside the nut that forms the seal, so tape is not required. If the threads on the valve are worn, a few wraps of tape can help, but do not use tape on the gasket itself.

Why is my supply line leaking after installation?

Check that the nuts are snug but not over-tightened, and that the line is not kinked. If the leak is at the valve, the gasket may be missing or the threads may be damaged.

Do I need to turn off the water to the whole house?

No, only the shut-off valve behind the toilet. If that valve does not work, turn off the main water valve for the house before starting the repair.