How to Replace a Toilet Supply Line in 30 Minutes or Less

TL;DR: Turn off the water at the shut-off valve behind the toilet, flush to empty the tank, unscrew the old supply line at both ends (tank and valve), wipe the threads, hand-tighten the new braided stainless line, then snug it with a wrench—no more than a quarter turn past hand-tight. Most leaks come from over-tightening or skipping the washer check. A $12 braided line lasts 10+ years versus 5-7 for plastic.

_Last reviewed: July 2026 · 6 min read_

A leaking toilet supply line can dump gallons onto your floor before you notice—especially if it starts while you're asleep or away. Most failures happen at the compression nut where the line meets the tank or the shut-off valve, and most happen because the line is old, kinked, or cheap plastic. Replacing a supply line before it fails is a 30-minute job that requires no plumbing license and costs less than a pizza.

Okoniq Property Hub logs every fixture swap with a photo and date, so you know exactly when you installed that new line and when to check it again.

What tools and parts do you need to replace a toilet supply line?

You need an adjustable wrench (or a 1/2" and 7/8" open-end wrench), a bucket or towel, and the new supply line. Most residential toilets use a 3/8" compression fitting at the shut-off valve and a 7/8" slip-joint nut at the tank tailpiece. Measure the distance from the center of the shut-off valve to the center of the tank inlet—most lines are sold in 12", 16", 20", or 24" lengths. Buy a braided stainless steel line with rubber washers at both ends; they cost $10-$15 and last a decade or more. Avoid the $3 vinyl or plastic versions—they crack in half that time.

If your shut-off valve won't turn or leaks when you try, this is the moment to replace it too. A quarter-turn ball valve costs $8 and installs with the same wrench; instructions are identical to the supply line swap. Okoniq lets you attach the valve receipt to the same task record so everything lives in one timeline.

How do you remove the old toilet supply line?

Turn off the water at the oval shut-off valve behind the toilet by rotating it clockwise until it stops—it should take a quarter to a half turn if it's a ball valve, or several full rotations if it's an old compression valve. Flush the toilet and hold the handle down to drain as much water as possible from the tank. Place a bucket or towel under the connections—there will be a few ounces of residual water in the line.

Loosen the slip-joint nut at the top (the tank end) first by turning it counterclockwise with your wrench. You may need to hold the tailpiece inside the tank with pliers to keep it from spinning, but most toilets have enough friction that the nut will break free on its own. Once the top nut is off, loosen the compression nut at the bottom (the shut-off valve end). The old line will come free, and water will drip from both fittings—that's normal. Wipe the threads at both the tank tailpiece and the valve outlet with a dry rag to remove sediment and old thread-seal residue.

How do you install the new braided supply line?

Check that the rubber washers are seated inside both compression nuts on the new line—one at each end. Hand-thread the bottom nut onto the shut-off valve outlet first, turning clockwise until it's snug. Then hand-thread the top nut onto the tank tailpiece the same way. Once both are finger-tight, use the wrench to snug each connection an additional quarter turn—no more. Over-tightening will crush the washer and cause a slow leak; under-tightening will let the nut back off over time. The sweet spot is when you feel resistance and the nut no longer turns easily by hand.

Turn the water back on slowly and watch both connections for drips. If you see a bead of water forming, turn the water off, loosen the leaking nut a quarter turn, check the washer orientation, and re-tighten. If the leak persists, the washer may be missing or damaged—remove the nut, inspect, and replace the washer if needed. Most hardware stores sell washer assortments for under $5. Once both connections are dry, flush the toilet twice and check again. Log the install date and the brand of the line in your maintenance tracker so you remember to inspect it in five years.

When should you replace a toilet supply line before it fails?

Replace any vinyl or plastic supply line immediately—they're rated for five years at best, and most fail closer to three if the water pressure is high or the line is kinked. Braided stainless lines are rated for 10-15 years, but inspect them every five years for corrosion at the fittings, cracks in the outer braid, or rust stains on the floor nearby. If your home was built before 2000 and the supply line has never been changed, assume it's original and swap it now. The same goes for any line that's been bumped by a toilet repair, moved during a floor refinish, or exposed to a previous leak—once the washer is compressed or the threads are stripped, the clock is ticking.

If you're replacing a wax ring or flange during a toilet reinstall, replace the supply line at the same time—it adds two minutes to the job and costs less than the service call to fix a leak six months later. Okoniq surfaces these bundled tasks automatically when you log a major fixture repair, so you don't forget the small stuff that prevents the next emergency.

FAQ

How tight should the compression nut be on a toilet supply line?

Hand-tight plus a quarter turn with a wrench. If you can't turn the nut by hand at all, it's too tight and you risk crushing the washer or cracking the valve threads. If it turns freely after the water is on, it's too loose—snug it another eighth turn and check for drips.

Can you reuse an old toilet supply line?

Technically yes if it's less than three years old, undamaged, and the washers are intact—but a new braided line costs $12 and eliminates the risk of a compression-set washer failing six months later. Reusing a vinyl line is never worth it; they harden with age and crack without warning.

What causes a toilet supply line to leak at the tank connection?

The most common cause is a missing or misaligned washer inside the slip-joint nut. The second is over-tightening, which crushes the washer and creates a gap once the pressure relaxes. The third is a corroded or cracked tank tailpiece—if the threads are visibly damaged, the tank will need a new fill valve assembly, not just a supply line swap.

Do you need Teflon tape or pipe dope on a compression fitting?

No—compression fittings seal with the rubber washer, not with thread sealant. Adding tape or dope can prevent the washer from seating properly and cause a leak. The only exception is if you're threading a male pipe thread into a female valve body (rare on toilet supply lines), in which case you'd use tape on the male threads only.

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

15-30 minutes if the shut-off valve works and you have the new line on hand. Add another 15 minutes if you need to replace a stuck or leaking shut-off valve at the same time. Budget an hour if it's your first time and you're making a hardware-store run mid-job.

This is educational information, not plumbing advice. If the shut-off valve is seized, the tank tailpiece is cracked, or you're not comfortable working near threaded brass fittings, call a licensed plumber to avoid a flood.