I had a leak under a new sink with new connections and tried to fix it by turning the nut tight. It didn’t work! I decided to try plumbers putty and it cured the problem.
What you’ll need
- Plumber’s putty (use “stain-free” on granite/marble/quartz; regular is fine on porcelain/metal)
- Adjustable wrench or channel-locks
- Bucket & towel
- Putty knife or plastic scraper
- Optional: silicone instead of putty for plastic drains or stone tops
Step-by-step
- Prep the area
- Place a bucket under the P-trap. Loosen the two slip-nuts and remove the trap.
- Unscrew the big locknut holding the drain body to the sink. Pull the drain pieces out from above and below.
- Clean the surfaces
- Scrape off old putty/silicone from the sink drain hole and flange (the top metal piece you see in the basin).
- Wipe everything dry. A clean, dry surface is key.
- Make the putty rope
- Pinch off some putty and roll a rope about the thickness of a pencil.
- Lay the rope under the lip of the drain flange (the underside that will touch the sink).
- Seat the flange
- Drop the flange into the sink hole from above and press firmly. You should see a small bead of putty squeeze out around the rim—good sign.
- Assemble from below
- From beneath, slide on the rubber gasket (against the sink), then any friction ring/washers (if your kit has them), then thread on the locknut.
- Hold the flange from above so it doesn’t spin. Tighten the locknut until snug—firm, but don’t overdo it (you can crack porcelain or distort the gasket).
- Align the opening
- If you have a pop-up drain, make sure the hole in the drain body faces the back of the sink so the lift-rod can pass through later.
- Clean excess putty
- From the top, wipe away the squeezed-out putty around the flange.
- Good news: plumber’s putty doesn’t need cure time—it’s ready immediately.
- Reconnect the trap
- Reinstall the tailpiece to the drain (if separate), then the P-trap.
- Ensure cone washers are oriented correctly (wide end toward the nut).
- Hand-tighten the slip-nuts, then give each an extra ¼ turn with pliers if needed.
- Leak test (two ways)
- Standing water test: Close the stopper, fill the basin. Check under the sink—if it drips now, the flange/putty seal needs a bit more locknut tension.
- Drain test: Pull the stopper and let it gush. If it leaks only while draining, the issue is likely the trap or slip-joint—snug the nuts or replace washers.
Tips & common pitfalls
- Stone countertops? Use stain-free putty or 100% silicone to avoid oil stains.
- Plastic drain bodies often seal better with silicone instead of putty (allow 12–24 hrs cure).
- Do not use putty on pressurized fittings or threaded water supply lines.
- If the locknut keeps loosening as you tighten, hold the flange from above with a rubber-gloved hand to prevent spinning.
- Persistent leaks at the trap? Replace the cone washers and check that cuts are square and parts aren’t cross-threaded.