Short definition

Cleaning P-traps annually means disassembling the U-shaped trap under each sink, flushing out hair, grease, and sediment, and reassembling. It’s a 10-minute DIY task per fixture, costs nothing if the slip nuts come apart, and prevents slow drains and odor. Skip it on old galvanized or brass traps that may break during disassembly.

What it is

The P-trap is the U-shaped pipe under every sink — see P-trap. It holds water that blocks sewer gas, but that same low spot collects hair, grease, soap scum, and grit over time. Annual cleaning empties the buildup before it slows the drain.

The procedure:

  1. Place a bucket under the trap to catch water and debris.
  2. Loosen the slip nuts at each end of the trap. Use channel-lock pliers on metal traps; for chromed plastic, hand-tight or a strap wrench to avoid scarring.
  3. Lower the trap and pour the contents into the bucket.
  4. Brush out the trap interior; flush with hot soapy water.
  5. Inspect each gasket / washer for cracks; replace if needed (under $5 at any hardware store).
  6. Reassemble — hand-tight plus a quarter turn. Don’t overtighten chromed plastic; it cracks.
  7. Run water and check for drips at both slip joints.

Common trap sizes are 1.25 in (lavatory) and 1.5 in (kitchen). Cadence: annually for most homes; every 6 months in kitchens with heavy cooking, and in long-hair or pet-washing households.

Why it matters to a homeowner

The case for the 10 minutes:

  • Slow kitchen drains are usually a P-trap full of grease and food particles, not a deeper clog. Pull, clean, reassemble — drains restored.
  • Bathroom basin slow drains are usually a hair-and-soap mass at the trap weir. Same fix.
  • Done annually, you avoid the recurring $200–$400 service call for a single-fixture clog.

When to call instead of DIY:

  • Old galvanized or brass traps that won’t disassemble — penetrating oil first; if still seized, call. Forcing it can break the tailpiece off the sink basket and turn a $0 task into a sink-strainer replacement.
  • Recurring slow drains every few months despite cleaning — the issue is upstream (branch line, vent, or main sewer). Auger or scope.
  • Drum traps (pre-1940 Seattle / Tacoma) — these are top-clean only, and replacing one triggers a permit because the trap geometry counts as scope change. See drum trap.
  • S-traps (pre-1970 stock) — banned under WA-amended UPC. Cleaning is fine; replacing requires a permitted retrofit to a P-trap with proper venting. See S-trap.

Common failure modes during the task

  • Cracked plastic slip nut from over-tightening — replace with a $5–$10 slip-nut kit.
  • Wrong-size replacement trap — match diameter and geometry (P vs S vs J).
  • Gasket missed or installed reversed — slow drip after reassembly.
  • Old corroded brass or galvanized seizing on disassembly — risk of breaking the basket strainer; call a pro.

Washington note

Septic households (1.1M+ in WA) — cleaning P-traps is septic-safe; just water and brush. Don’t pour caustic drain cleaners as part of the task; they kill the bacteria the drainfield needs.

Cedar/Tolt soft-water households (Seattle, much of King County) see less internal scale, so the buildup is hair and grease. Eastside and Spokane hard-water households (12–25 GPG) accumulate calcium scale faster — a vinegar pre-soak before disassembly helps loosen mineral deposits at the slip joints.

Pre-1940 Seattle and Tacoma stock often has drum traps instead of P-traps in some bathrooms. Don’t try to clean a drum trap with the P-trap procedure; the cap is on top, and the cleanout sequence is different.

Cost data

  • Materials (gaskets, brushes): $5–$20 once a year.
  • Replacement P-trap kit if old one cracks during disassembly: $10–$30.
  • DIY only — no pro cost when it goes well.