Short definition

Clogged drain causes vary by fixture: hair in bathrooms, grease in kitchens, paper and “flushable” wipes in toilets, and tree roots or pipe failure in the mainline. The fixture pattern — one drain slow, multiple drains slow, or all drains plus a basement backup — tells you the scale of the problem before you pick up a tool.

What it is

The first diagnostic question on any clog is: how many fixtures are affected?

  • One fixture slow. The clog is in that fixture’s branch drain — its P-trap or branch arm. Almost always DIY: pull the pop-up, snake the trap.
  • Multiple fixtures on the same level slow. The clog is in a vertical-to-horizontal branch that serves the group. Larger snake, sometimes pro.
  • All fixtures slow plus a backup at the lowest fixture (basement floor drain, bathtub on the lowest floor). The clog is on the mainline or side sewer. Stop DIY and call a sewer specialist with a camera.

Then narrow by fixture type:

  • Bathroom sink — hair plus soap scum at the pop-up assembly.
  • Kitchen sink — grease plus food residue.
  • Tub or shower — hair plus body oils plus soap scum at the trip-lever or trap.
  • Toilet — paper, “flushable” wipes, foreign objects, or partial trap clog.
  • Floor drain — debris, dried-up trap (no water in the seal), sediment.
  • Mainline / side sewer — tree roots (Doug fir, western red cedar, big-leaf maple in PNW), grease, paper accumulation, or pipe failure (Orangeburg, clay-tile, cast-iron).

Why it matters to a homeowner

The fixture pattern decides what tool you reach for and whether DIY is reasonable. A bathroom hair clog is two minutes with a Zip-It strip. A whole-house slow drain with a basement backup is a $400-$700 sewer specialist call — and aggressive DIY snaking can break a cable inside an old clay or Orangeburg pipe and turn it into a $1,500 retrieval plus the original problem still unsolved.

When a plumber asks “is just one drain slow, or all of them?” they’re triaging exactly this question. Save time on the call by walking through the house first.

Common failure modes by fixture

  • Hair (bathroom). Pop-up assemblies and tub overflow linkage.
  • Grease and FOG (kitchen). Cools and adheres to pipe walls.
  • Soap scum plus body oils (tub/shower). Combines with hair.
  • Wet wipes / paper towels / non-flushable items (toilet, mainline). Even “flushable” wipes don’t break down.
  • Tree roots (mainline). PNW signature; Doug fir, cedar, and big-leaf maple are the biggest offenders.
  • Pipe scale / mineral buildup. Hard-water areas, slow whole-house pressure drop.
  • Orangeburg pipe collapse. Seattle 1945–1972 sewers.
  • Cast-iron channel and scale buildup. Pre-1970 PNW DWV.
  • Sagging belly in the side sewer. Recurring clog at the same spot weeks after snaking.

Common variants

  • Slow drain (partial blockage) vs. backed-up drain (full blockage). Same cause, different urgency.
  • Single-fixture vs. multi-fixture vs. mainline backup. Different scope, different tool, different bill.
  • Clog vs. vent issue. Gurgling without a slow drain often means a vent obstruction (bird’s nest, ice plug), not a drain clog.

Washington note

Two PNW patterns matter most. First, tree roots in side sewers — Doug fir, western red cedar, and big-leaf maple have aggressive root systems that find every clay-tile or Orangeburg joint. Recurring clogs at the same time of year (often early summer) usually mean roots. Second, Orangeburg pipe collapse — bituminized fiber pipe widely installed in Seattle from 1945 to the early 1970s deforms ovally under soil load and eventually fails. A camera scope distinguishes roots (tendrils visible at joints) from Orangeburg (soft, out-of-round walls) and decides whether you can keep snaking or need replacement.

For mainline backups in WA, especially in pre-1970 Seattle and Tacoma neighborhoods: get the camera scope before the snake.