Install a Toilet Supply Line

Water reaches your toilet through a single flexible line connecting the wall shutoff valve to the tank inlet. This supply line fails more often than any other plumbing component in a bathroom — not because the installation is difficult, but because rubber washers compress over time and cheap braided lines develop pinhole leaks at the crimped fittings. Replacing a supply line before it fails saves you from mopping up a slow flood at 2 AM. A proper installation means hand-tight connections with quality washers, the right length line to avoid kinking, and a shutoff valve that actually shuts off. Most toilet leaks trace back to this single connection, which makes knowing how to replace it correctly one of the highest-value skills in home maintenance.

1. Stop Water Flow First. Turn the oval shutoff valve clockwise until it stops. Flush the toilet and hold the handle down to drain most of the tank water. Use a sponge or towel to soak up the remaining water in the bottom of the tank where the supply line connects.
2. Disconnect Both Ends. Place a bucket or towel under the connection point at the wall. Use an adjustable wrench to loosen the coupling nut at the shutoff valve, turning counterclockwise. Unscrew it by hand once loose. Move to the tank connection and repeat, loosening the nut that threads onto the toilet shank. Pull the old line free.
3. Get the Right Length. Measure the distance from the center of the shutoff valve outlet to the center of the toilet shank on the bottom of the tank. Add two inches to allow for the bend. Braided supply lines come in fixed lengths — choose the next size up from your measurement rather than forcing a too-short line to stretch.
4. Verify Washers Are Fresh. Inspect both coupling nuts on your new supply line for pre-installed rubber washers. These flat rings create the watertight seal and should be soft, not cracked or flattened. If your line didn't come with washers or they look compressed, buy new ones sized to match your fittings before proceeding.
5. Connect to Shutoff Valve. Thread the lower coupling nut onto the shutoff valve outlet by hand, turning clockwise. The washer should compress slightly as you tighten. Once hand-tight, use the adjustable wrench to give it a quarter-turn more. Stop when you feel firm resistance — overtightening crushes the washer and causes leaks.
6. Thread Tank Connection. Route the supply line upward with a gentle curve, avoiding sharp bends. Thread the upper coupling nut onto the threaded shank protruding from the tank bottom. Hand-tighten, then add a quarter-turn with the wrench. The line should have a smooth arc with no kinks or tension pulling the tank connection sideways.
7. Check for Leaks Now. Turn the shutoff valve counterclockwise to restore water flow. Watch both connections as the tank fills. Look for drips forming at either coupling nut or moisture spreading from the threads. If a connection weeps, turn off the water and tighten that nut another eighth-turn. Let the tank fill completely and flush twice, checking again during refill.
8. Verify and Document. Once both connections stay dry through two fill cycles, check that the supply line hangs with a relaxed curve and doesn't contact any other pipes or the wall. Wipe down all fittings and the floor. Mark your calendar to inspect this connection again in six months — a quick visual check catches slow leaks before they cause damage.