P-Trap Maintenance — Fix Leaks, Clogs & Smells Under Any Sink
The curved pipe under your sink does two jobs — catches debris and blocks sewer gas. Here's how to keep it working.
Safety first: 💡 Always place a bucket under the P-trap before loosening any slip nut — even a 'dry' trap holds about a cup of water plus whatever debris has collected.
What a P-Trap Does
The P-trap is the U-shaped pipe under every sink, tub, and shower. It holds a small pool of water that seals off the drain line — that water is the only thing stopping sewer gas from rising into your home. It also catches dropped jewelry, hair, and food scraps before they reach the main line.
Signs Your P-Trap Needs Attention
Sewer or rotten-egg smell coming from the drain, slow draining, gurgling sounds when other fixtures run, visible drips onto the cabinet floor, water stains under the sink, or standing water in the cabinet base. Any of these means the trap is clogged, leaking, or has dried out.
Fixing a Slow or Clogged P-Trap
Turn off the faucet, place a bucket under the trap, and loosen both slip nuts by hand (or with channel-lock pliers wrapped in tape to protect the finish). Pull the trap down, empty it, and clean out gunk with a bottle brush and hot soapy water. Rinse, reinstall, and hand-tighten the slip nuts a quarter turn past snug — overtightening cracks the plastic threads.
Stopping a Leaking P-Trap
Most leaks come from a compressed or missing slip-joint washer, cross-threaded nuts, or a cracked trap arm. Disassemble, inspect each nylon washer, and replace any that look flattened or torn (a full kit is under $5). Reassemble with the washer's beveled edge facing the trap. If the trap itself is cracked, replace the whole assembly — don't caulk it.
Eliminating Sewer Smells
If the sink is rarely used (guest bath, basement, utility sink), the trap water evaporates and lets gas through. Run water for 30 seconds once a week, or pour a cup of water plus a tablespoon of mineral oil down the drain to slow evaporation. If the smell persists after refilling, the trap is clogged with biofilm — pull it and scrub, or the vent stack on the roof is blocked and needs a plumber.
Kitchen vs Bathroom P-Traps
Kitchen P-traps clog with grease and food; scrub monthly and never pour bacon fat down the drain. Bathroom P-traps clog with hair, soap scum, and toothpaste; use a hair-catcher strainer and clean the trap every 6 months. Both use the same 1-1/4 inch (bathroom) or 1-1/2 inch (kitchen) slip-joint fittings.
When to Replace vs Clean
Clean when it's just debris and washers look intact. Replace when the plastic is cracked, threads are stripped, nuts won't stop leaking after new washers, or the trap arm has visible corrosion (metal traps). A full plastic P-trap assembly runs $6–$15 at any hardware store.
When to call a pro
- Sewer smell that returns within a day of refilling the trap (indicates blocked vent stack)
- Water backing up into other fixtures when you run the sink
- Cast iron or corroded metal traps that crumble when touched
- Leaks that continue after replacing washers and the trap itself
- P-trap missing entirely or connected with flexible accordion tubing (code violation in most areas)
Frequently asked questions
How often should I clean my P-trap?
Kitchen P-traps: every 3–6 months, or immediately if drainage slows. Bathroom P-traps: every 6–12 months. Rarely used sinks: run water weekly to keep the trap seal from evaporating.
Why does my P-trap keep clogging?
In kitchens it's almost always grease solidifying as it cools — even 'drain-safe' cooking oil hardens in the trap. In bathrooms it's hair binding with soap scum. A mesh drain strainer prevents 90% of clogs.
Can I use Drano on a P-trap?
Not recommended. Chemical drain cleaners sit in the trap and can etch plastic threads, corrode metal, and damage rubber washers — often causing the leak they were meant to prevent. Manual cleaning is faster and safer.
How much does a plumber charge to replace a P-trap?
Typical service call is $150–$300 for a standard sink P-trap swap. If they also need to snake the branch line or replace the trap arm inside the wall, expect $300–$600.
Why does my P-trap smell like sewer gas?
Three causes: (1) the water seal evaporated — refill it, (2) biofilm buildup is off-gassing — clean the trap, or (3) the vent stack is blocked and siphoning water out of the trap — that needs a plumber.
Is a flexible accordion P-trap OK?
No. Accordion-style flexible traps are banned by most plumbing codes because their ridges collect debris and clog constantly. Always use a smooth rigid P-trap assembly.