Quick answer: Replacing a toilet supply line means isolating water at a working shutoff, verifying the tank and connector are dry, removing a damaged/kinked/corroded connector, installing a new braided or rigid connector with matching ends (commonly 3/8″ compression at the stop and 7/8″ ballcock at the fill valve), snugging without overtightening plastic shanks, then repressurizing slowly and checking both couplings for leaks. Manufacturer install sheets and local plumbing code control the exact fittings — do not invent torque values or force a seized stop.
This guide is only about the flexible or rigid connector between the toilet angle stop and the fill-valve shank. If the shutoff itself leaks, sticks, or will not close, stop here and use toilet shutoff valve leaking, stuck or won’t close. If the fill valve is the worn part, use how to replace a toilet fill valve instead of treating every drip as a hose problem.
What a supply line does — and when to replace it
The supply connector carries pressurized water from the stop into the tank. Homes commonly use stainless-steel braided flex lines or older chrome/rigid tubing. Replace the connector when you see:
- Visible kinks, crushed braid, or bulging under the sleeve
- Corroded, rounded, or cracked coupling nuts
- Persistent drip at either end after a careful snug (and the stop/fill valve threads are sound)
- Age plus disturbance — for example, you are already replacing the fill valve and the old line is stiff or damaged
Do not treat a packing-nut weep on the stop body, a cracked fill-valve shank, or a tank-to-bowl gasket drip as a “new hose will fix it” job. Wipe the area dry, open the stop slowly, and watch where water reappears before you buy parts.
Educational illustration — diagram for teaching, not a photo of a real repair.
Connector design notes: compression vs ballcock ends
Most modern toilet connectors are labeled by the two ends:
- Shutoff end: often a metal 3/8″ compression nut that mates to the angle stop. Maker sheets for Click Seal–style lines typically call for threading the metal nut onto the stop and tightening about one-half turn beyond hand-tight, then checking for leaks without cranking.
- Fill-valve (ballcock) end: often a 7/8″ coupling for the threaded shank under the tank. Many plastic nuts are designed for hand-tightening only. Some systems click at a torque stop so you do not crush the shank — Fluidmaster’s Click Seal toilet connector instructions explicitly warn against overtightening and note tools are not needed for the plastic Click Seal nut.
Braided stainless flex lines tolerate slight misalignment and are common for DIY swaps. Rigid chrome or copper connectors still appear in older installs; they require correct length and alignment and are less forgiving of offset stops. Neither style is “universally better” in every bathroom — match end sizes, length (leave a gentle curve, not a sharp kink), and whatever your local code and the toilet/fill-valve maker allow. For unlabeled hardware, use the package instructions rather than assuming brand-specific requirements.
| End | Common size | Typical snug practice (per maker sheets) | Failure cue |
|---|---|---|---|
| Angle stop | 3/8″ compression (common) | Metal nut: often ~½ turn past hand-tight | Weep at ferrule; stripped threads; seized stop |
| Fill valve shank | 7/8″ ballcock (common) | Plastic nut: hand-tight / click-stop; no cheater bar | Cracked shank; crushed washer; drip under tank |
| Universal adapters | Multi-size kits | Only as labeled for your stop | Wrong adapter masquerading as a “fit” |
Safety first
- Shut off water at the toilet stop and prove the tank stops filling. If the stop is frozen or corroded, do not force it — isolate at the house main and follow the shutoff guide linked above.
- Flush, hold the handle if needed, and sponge remaining tank water so disconnecting the line does not dump a bowl of water onto the floor.
- Protect flooring; keep a towel under the stop and under the tank shank.
- Never overtighten plastic fill-valve nuts or force corroded stop threads. Overtightening is a common way to crack shanks and start floods.
- Manufacturer instructions and local plumbing code control permitted materials and connections. Follow manufacturer instructions and local plumbing requirements; use a licensed plumber or inspector when required.
- If you open a stop that will not close, you can create a continuous spray — know where the main shutoff is before you start.
Educational illustration — diagram for teaching, not a photo of a real repair.
Tools and materials
- New toilet supply connector with matching ends and adequate length
- Adjustable wrench for metal stop nuts (and only where the maker allows tools)
- Bucket/towels/sponge; flashlight
- The connector’s install sheet (and the fill-valve sheet if you are also servicing the valve)
- Optional: replacement fill-valve cone/flat washers only if the kit requires them — do not improvise putty on supply threads
Step-by-step replacement
- Isolate and verify dry. Close the toilet stop. Flush to drop tank level. Confirm the fill valve is not still refilling. If water keeps entering, the stop is not holding — stop the DIY connector swap and isolate at the main.
- Relieve pressure. With the stop closed and the tank mostly empty, briefly open the fill path if needed so the connector is not under full line pressure when you crack the nuts (practice varies; never open fittings on a free-flowing seized stop).
- Disconnect the fill-valve end. Support the valve shank with one hand. Back off the coupling nut. Catch residual water. Inspect the shank threads and any washer for damage.
- Disconnect the stop end. Hold the stop body steady if the maker advises against twisting the valve. Remove the old connector. Clean old sealant crumbs or deformed ferrules only as appropriate for compression fittings — do not score soft copper.
- Match the new connector. Confirm length (a slight sag/curve is fine; a kink is not). Confirm the stop end and ballcock end match your hardware. Discard connectors with damaged braid or cracked nuts.
- Install the stop end. Thread the metal compression nut onto the stop per the sheet. A common Fluidmaster Click Seal instruction pattern is metal nut to the shutoff, then about one-half turn beyond hand-tight — then check for leaks rather than chasing “tighter forever.”
- Install the fill-valve end. Align threads carefully. For Click Seal–style plastic nuts, the maker directs you to align threads (including a counter-clockwise align step on some sheets), then hand-tighten until the nut clicks. Do not put a wrench on plastic click nuts unless that specific product says otherwise.
- Repressurize slowly. Open the toilet stop gradually. Listen for spray. Wipe both couplings completely dry.
- Leak check. Watch for two to five minutes at rest, then flush several times and recheck. A new drip at the stop may mean the ferrule/nut needs a slight additional snug — or that the stop itself is failing. A drip at the tank shank often means cross-threading, a missing washer, or overtightening damage.
- Final set. Confirm the fill valve shuts off at the correct waterline and that the connector is not rubbing a sharp cabinet edge that will saw into the braid over time.
What not to do
- Do not force a seized or heavily corroded shutoff with a cheater bar.
- Do not overtighten plastic ballcock nuts “just to be safe.”
- Do not reuse a badly kinked braided line or a cracked nut.
- Do not use plumber’s putty as a substitute for the correct compression/ballcock seal (fill-valve makers commonly forbid putty on these fittings).
- Do not assume one “universal” connector fits every stop without reading the end markings.
- Do not pitch bowl cleaners or tank tablets as a fix for a mechanical supply leak.
When to call a plumber
- The toilet stop will not close, weeps from the body/packing, or crumbles when turned
- Threads on the stop or fill-valve shank are stripped
- You need a new angle stop (sweat, PEX, or push-fit work beyond your skill/permit)
- Repeated leaks after a careful connector swap
- Any sign of floor damage from a long-running drip
Misdiagnoses to avoid
- Running toilet: usually flapper/flush valve/fill valve — not the supply hose.
- Dampness under the tank joint: tank-to-bowl gasket or tank bolts, not the supply connector.
- Puddle at the floor flange: wax/flange path — see the wax-ring and flange guides in the related guides.
FAQ
Should I replace the supply line whenever I replace the fill valve? Often yes if the old line is stiff, corroded, or the wrong length — but only after the stop closes reliably.
Braided or rigid? Both can work when ends match and installation follows the sheet and local code. Braided flex is usually easier for DIY alignment; rigid lines demand accurate length.
How tight is tight enough? Follow the connector manufacturer. A widespread pattern is metal stop nut about half a turn past hand-tight, plastic ballcock nut hand-tight or to a click — then leak-check, don’t crush.
Can I leave the water on and just swap quickly? No. Always shut off and verify. A free-flowing open stop can flood a room in minutes.
Sources
- Fluidmaster — Click Seal supply line instructions / FAQs
- Fluidmaster — Click Seal toilet connector installation sheet (PDF)
- Fluidmaster — Click Seal toilet installation instructions (PDF, alternate revision)
- Fluidmaster 400A fill valve instructions — supply connection / do not overtighten (PDF)
- EPA WaterSense — Fix a Leak Week
Related guides
- Toilet shutoff valve leaking, stuck or won’t close
- How to replace a toilet fill valve
- How to replace a toilet wax ring (next step if the wet zone is at the floor, not the supply)