Quick answer
The best toilet supply line for most homes is a 12 in braided stainless connector in the standard 3/8 in compression x 7/8 in ballcock size: if you are replacing a plain plastic or vinyl line, buy the Eastman 48088 12 in Steel-Flex Toilet Connector, rated 4.6 stars across 4,705 Amazon ratings. Its listing states a 125 psi working pressure and a 2,500 psi burst figure. Measure from the valve outlet to the tank inlet before you order. Snug the tank-side nut by hand, because it threads onto the fill valve's plastic shank, and put a leak sensor on the floor behind the toilet.
Buyer's Guide
What to know before you buy.
Why Toilet Supply Lines Fail
A toilet supply line is under full house pressure every minute of the day, flushed or not. That makes it one of the few hoses in a home that can leak for hours with nobody watching, often overnight or while you are away. Old lines fail in a handful of familiar ways. A solid plastic or vinyl line turns brittle and can crack at its nut. A plastic coupling nut that was cranked down with pliers can split later, not always on the day it went on. A braided line can corrode at a crimp, fray where it rubs the floor, or bulge when the core underneath has aged. The steel braid is only a jacket. The water still runs through a plastic or rubber tube inside it, which is why even a braided line needs checking and, eventually, replacing.
Size: What 3/8 x 7/8 Means
Every listing on this page describes the same size: 3/8 in compression at one end and 7/8 in ballcock at the other. The 3/8 in compression end screws onto the outlet of the shutoff valve on the wall or floor, often called the angle stop. The 7/8 in ballcock end threads onto the bottom of the fill valve, the plastic shank that pokes out under the tank. Those numbers name the threads, not the width of the hose, so a 3/8 x 7/8 line fits most US toilets whatever the brand. Look at the old line's nuts before you order. If the valve end is bigger, as on some older 1/2 in valves, you need a connector made for that size. Among the listings read for this page, lengths ran from 6 in to 24 in.
Length: Measure the Route, Then Add a Little
Length is the part people get wrong. Measure from the face of the valve outlet to the bottom of the fill-valve shank, following the curve the line will take rather than a straight line between the two points. PLUMBINGMASTER's listing gives a simple rule: add a couple of inches, so a 10 in measurement means ordering 12 in. A line that is too short pulls sideways on both nuts, and a sideways load is how a washer unseats. One that is far too long ends up in a loop that can kink, which is why the 24 in HIGHCRAFT belongs only where the valve sits well off to one side. When the valve is directly below the inlet, Fluidmaster's 9 in version (B1T09) avoids a loop. Never join two lines with a coupler, since every extra joint is another place for a drip to start.
How Tight: Hand-Tight at the Tank
Tighten the two ends differently. At the tank, the nut threads onto the fill valve's plastic shank, so turn it by hand until it is snug and stop there; a wrench can crack the shank or a plastic nut, and that crack may not show for days. At the valve, a metal compression nut usually goes on hand-tight and then gets a small extra turn with a wrench, while a second wrench holds the valve body so it does not twist on its pipe. These connectors seal on the rubber washer inside each nut, not on the threads, so thread tape is normally unnecessary. Open the valve slowly, flush twice, then wipe each nut with a dry tissue. EPA WaterSense suggests checking pipe fittings for water on the outside, and a damp spot here calls for a quarter turn more at that nut, not a full turn.
The Valve, the Travel Habit and the Sensor
A new line is only as useful as the valve behind it. Before you swap the line, close the shutoff valve and flush: if the tank keeps refilling, the valve does not close, and replacing it comes first. Old multi-turn valves often seize, or start to weep at the stem once they are finally moved, which is a common reason a ten-minute job grows. Once everything is sound, build two habits. Close the toilet valve, or better the main, before you leave home for more than a few days, so the line holds no pressure while nobody is there. And put a battery leak alarm on the floor behind the toilet, where a dripping nut shows first. A smart shutoff valve on the main goes further and closes the water when its sensor gets wet. EPA's mold guide says wet materials dried within 24 to 48 hours will, in most cases, not grow mold.
Who Does Not Need a New Supply Line
A new supply line fixes one thing: water coming from the line or its two nuts. Water at the base of the toilet after a flush usually points to the wax ring or a loose bowl, which our guide to a toilet leaking at the base covers. A toilet that runs or refills on its own is leaking inside the tank, most often at the flapper; EPA WaterSense suggests a few drops of food coloring in the tank, and if color shows in the bowl after 10 minutes, you have a leak. Drips from the tank bolts call for new bolt washers. Beads of water all over the tank and line on a humid day are condensation. If the shutoff valve drips at its stem or will not close, the valve needs replacing, a plumber's job when it is soldered on. Water already coming through the ceiling below means shutting the water off and drying first.
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