The toilet supply line is the flexible hose that runs from the shutoff valve on the wall or floor to the fill valve on the bottom of the toilet tank. It is the most common source of toilet leaks that are not inside the tank. A supply line that drips at either connection, has a cracked plastic nut, or is bulging from age needs replacement before it fails completely. A burst supply line floods a bathroom in minutes.
Replacing a toilet supply line takes 10 to 15 minutes, costs $6 to $12 for a braided stainless steel replacement, and requires one wrench. Here is how to remove the old one, choose the right replacement, and install it so it does not leak.
Choosing the Right Replacement Supply Line
Buy a braided stainless steel supply line. Do not buy a plastic supply line. Plastic lines become brittle with age and crack at the nuts. Braided stainless steel lines are flexible, durable, and rated for decades of service. The price difference is $3 to $5. This is not the place to save money.
Measure the length you need. Standard toilet supply lines are sold in lengths of 9 inches, 12 inches, 16 inches, and 20 inches. Measure from the shutoff valve outlet to the fill valve inlet on the bottom of the toilet tank with the line following its natural curve. Add 2 to 3 inches to your measurement so the line has a gentle curve without kinking or pulling tight. A line that is too short pulls at the connections and leaks. A line that is too long loops awkwardly and collects dust. A 12-inch line fits most standard toilets where the shutoff valve is directly below the tank. A 16-inch or 20-inch line is needed when the shutoff valve is offset to the side or lower on the wall.
Check the connector size at both ends. Toilet supply lines have one of two connector sizes. A 7/8-inch ballcock nut connects to the fill valve shank on the bottom of the toilet tank. This is the standard size for almost all toilets. A 3/8-inch or 1/2-inch compression nut connects to the shutoff valve. The 3/8-inch is the most common size for residential shutoff valves. The 1/2-inch is used on some older valves. If you are unsure, buy a supply line labeled toilet supply line with 7/8-inch by 3/8-inch connections. This fits the vast majority of toilets and shutoff valves. If the shutoff valve outlet looks larger than standard, it may be 1/2-inch. Bring the old supply line to the store to match the connections.
Step One: Remove the Old Supply Line
Turn off the water at the shutoff valve behind the toilet. Turn the valve clockwise until it stops. Flush the toilet to empty the tank. Hold the flush handle down to drain as much water as possible. Sponge out the remaining water from the bottom of the tank. The less water in the tank, the less water drips onto the floor when you disconnect the supply line.
Place a small bowl or towel under the shutoff valve. Unscrew the supply line nut at the shutoff valve. Turn the nut counterclockwise. If the nut is plastic, use your hand. If the nut is metal or is stuck, use an adjustable wrench. Water will drain from the supply line into the bowl. Unscrew the supply line nut at the fill valve on the bottom of the toilet tank. This nut is usually plastic and should be loosened by hand. If it is tight, use an adjustable wrench gently. The plastic threads on the fill valve shank will strip if you apply too much force. Hold the fill valve body inside the tank with one hand while turning the nut underneath with the other. This prevents the fill valve from rotating and loosening its own mounting nut.
Step Two: Install the New Supply Line
Connect the new supply line to the fill valve first. The fill valve connection is a plastic nut with a rubber washer inside. The washer creates the seal against the fill valve shank. No Teflon tape is needed on this connection. The rubber washer does the sealing. Teflon tape on a gasketed connection can prevent the nut from threading far enough to compress the washer. Thread the nut onto the fill valve shank by hand. Tighten it hand-tight, then an additional quarter turn with your hand. Do not use a wrench on the plastic fill valve nut. The rubber washer seals with hand pressure. Overtightening cracks the plastic nut or the fill valve shank.
Connect the other end of the supply line to the shutoff valve. This connection may have a rubber washer inside the nut or may be a compression fitting that requires Teflon tape. Most braided stainless steel supply lines have a rubber washer and require no tape. If the shutoff valve outlet has a flat face, the supply line nut has a rubber washer inside and seals without tape. If the shutoff valve outlet has a tapered compression fitting, wrap the male threads on the valve with two to three turns of Teflon tape before threading the nut on. Tighten with an adjustable wrench until snug, then an additional quarter turn. Do not overtighten a compression fitting. The ferrule or washer creates the seal, not brute force.
Hand-bend the supply line into a smooth curve. The line should not kink, twist, or press against the toilet bowl or the wall. A braided stainless steel line holds its shape when gently curved. If the line is too long, a single wide loop absorbs the extra length without kinking. If the line kinks, it is too short. Buy a longer one.
Step Three: Turn the Water On and Check for Leaks
Open the shutoff valve slowly. Listen for water flowing. Watch both connections as the tank fills. A few drops of water at a connection that stop when you tighten the nut slightly are normal. A steady drip that continues after tightening means the connection is not sealed. Close the valve, loosen the nut, check that the rubber washer is seated correctly and is not pinched or missing, and retighten.
Check for leaks again after the toilet has been flushed once. The brief pressure change from the fill valve opening and closing can reveal a connection that is not quite tight enough. A connection that drips only when the toilet is flushed needs an additional quarter turn on the nut.
Leave the bowl or towel under the valve for the first hour after installation to catch any slow drips that are not immediately visible. A connection that seeps just enough to dampen the supply line but not enough to drip onto the floor can go unnoticed until the water damage appears. The bowl under the valve is cheap insurance.
When to Replace a Supply Line Before It Fails
Replace the supply line if it is plastic and more than 5 years old. Plastic supply lines are the most common cause of toilet-related water damage. They fail at the nuts, which crack from repeated temperature cycling and water pressure changes. Replace any plastic supply line with a braided stainless steel line immediately. Do not wait for it to leak.
Replace the supply line if the braided stainless steel jacket is bulging, rusted, or has visible kinks. A bulge in the braided jacket indicates the inner tube has weakened at that point and is ballooning under pressure. It will burst. A rusted braided jacket indicates the stainless steel is corroding, typically from exposure to a slow leak or cleaning chemicals. The inner tube will fail when the jacket can no longer contain it. A kinked supply line has a damaged inner tube that will eventually crack at the kink point.
Replace the supply line if the connection nuts are cracked, stripped, or leaking and cannot be tightened enough to stop the leak. A cracked nut is a failure, not a maintenance issue. It must be replaced, not retightened.
Replace the supply line any time you replace the toilet, the shutoff valve, or the fill valve. A new supply line costs $8. Reusing an old supply line on new equipment saves $8 and risks a leak that damages the floor, the subfloor, and the ceiling below. The economics of reusing a supply line do not work.
Frequently Asked Questions
I replaced the supply line and it still leaks at the fill valve connection. What did I do wrong?
The rubber washer inside the supply line nut is missing, pinched, or not seated correctly. Unscrew the nut and check. The washer is a small black rubber ring inside the nut. It sometimes falls out during packaging and ends up loose in the bag. If the washer is missing, the connection will leak no matter how tight you make the nut. If the washer is pinched or folded, it cannot create an even seal. Remove it and reseat it flat in the nut.
Should I use a rigid supply line instead of a flexible one?
No. Rigid chrome-plated copper or brass supply lines are obsolete. They are difficult to install, require exact measurements for the offset between the valve and the fill valve, and cannot be adjusted if the toilet shifts. A flexible braided stainless steel line is the correct choice in all modern installations. The only reason to use a rigid supply line is historical accuracy in a period restoration. For every other purpose, flexible is better.
Is a toilet supply line the same as a faucet supply line?
No. Faucet supply lines are typically 3/8-inch compression on one end and 1/2-inch FIP, or female iron pipe, on the other. Toilet supply lines are 3/8-inch compression on one end and 7/8-inch ballcock on the other. The connections are not interchangeable. A faucet supply line will not fit a toilet fill valve, and a toilet supply line will not fit a faucet. The packaging is clearly labeled. Buy the line labeled for toilets.
Last modified: June 20, 2026
