Slow or Clogged Drain — Causes & How to Fix It

Why is my drain slow or clogged and how do I unclog it?

Most slow drains come from hair, grease, soap scum, or food building up in the trap or branch line, and you can usually clear them with a plunger, a drain snake, or by cleaning the P-trap. Whole-house backups or sewage smells point to a main line problem that needs a pro.

ℹ️ Reference only: For general reference only. This guide does not guarantee any result — every home is different. Verify against your local building codes and a licensed professional before acting, especially for electrical, gas, plumbing, structural, or roof work.

💵 DIY: $0–$30 (plunger, plastic hair tool, or a basic hand auger). Pro: roughly $125–$300 to clear a single drain or trap; $200–$650 for a main line auger; $400–$900+ for hydro-jetting; $250–$550 for a sewer camera inspection. Costs vary by region and severity. ⏱ 15–45 minutes for a plunger, trap cleaning, or snaking a single drain. Add time if you need to buy a tool. ● Use caution

Safety: If you've already poured a chemical drain cleaner in, do NOT open the P-trap or plunge — the caustic water can splash your skin and eyes; wear gloves and eye protection and let a plumber handle it. Don't use boiling water on PVC pipes, and never mix drain-cleaning chemicals (it can release toxic gas). Standing water plus electricity is a shock risk — turn off the garbage disposal at the breaker and unplug it before reaching into a kitchen drain, and never reach into a disposal with your hand. Don't clear a roof vent stack yourself; roof-height work belongs to a pro.

Common causes

Hair and soap scum buildup in bathroom sink, tub, and shower drains — the single most common cause, usually caught right at the stopper or a few inches down. (most common)
Quick check: Pull the pop-up stopper or remove the tub/shower strainer and look for a hair clump; shine a flashlight down the drain.
Grease, fat, and food scraps in the kitchen sink line — grease congeals on pipe walls and traps debris over time. (most common)
Quick check: Note if it's only the kitchen sink that's slow and whether it worsened after cooking; run hot water and listen for slow drainage.
Object or debris stuck in the P-trap (the U-shaped pipe under the sink) — jewelry, toothpaste caps, gunk. (common)
Quick check: Look under the sink; if water drains fine elsewhere but not this one fixture, the trap is the likely spot.
A clogged or sticking sink stopper / pop-up assembly that isn't fully opening. (common)
Quick check: Lift the pop-up by hand or remove it; if the drain runs fast with the stopper out, the stopper is the problem.
Partial blockage in the branch line beyond the trap (the horizontal pipe running to the main). (common)
Quick check: If a plunger and trap cleaning don't help but only one fixture is affected, the clog is deeper in that branch.
Main sewer line blockage — tree roots, collapsed pipe, or heavy buildup. Affects multiple fixtures at once. (less common)
Quick check: Check if flushing a toilet makes the tub gurgle or back up, or if the lowest drains (basement, ground-floor tub) overflow — that signals the main.
Blocked vent stack (the pipe through the roof) — clogged by debris or a nest, or frozen shut in deep-freeze climates — causing slow, gurgling drains throughout. (less common)
Quick check: Listen for gurgling and notice slow draining across many fixtures with no visible clog in any trap.

How to fix it

Try a plunger first. For a sink, block the overflow hole (and the second basin in a double sink) with a wet rag, fill enough water to cover the plunger cup, and plunge firmly 10–15 times. This clears most simple clogs without chemicals.
Clean the P-trap. Put a bucket under the U-shaped pipe, unscrew the two slip nuts by hand or with channel-lock pliers, dump and clean out the trap, then reassemble. This catches hair clumps and dropped objects.
Use a drain snake / hair-clog tool. A cheap plastic 'zip-it' barbed strip pulls hair out of bathroom drains. For deeper clogs, feed a hand auger (drain snake) down the drain or into the trap arm, crank to catch the clog, then pull it back out.
Pull and clean the stopper. Remove the sink pop-up or tub stopper (often a small nut behind the sink, or a screw under a tub overflow plate) and clear the hair and gunk wrapped around it.
For grease in a kitchen line, after clearing flush with very hot tap water (not boiling — boiling can soften PVC and loosen joints) plus dish soap, then run hot water a minute. Avoid pouring grease down the drain going forward.
Skip or minimize chemical drain cleaners. They often don't fully clear clogs, can damage older or PVC pipes, and the caustic water left sitting is dangerous if you later open the trap. If you must, follow label directions exactly and never mix products.
If multiple fixtures back up, the lowest drains overflow, or a toilet makes the tub gurgle, stop DIY and call a plumber — that's a main line issue needing a powered auger or camera inspection.

DIY or call a pro?

A single slow fixture is squarely DIY: plunger, P-trap cleaning, and a hand snake solve the large majority of these for a few dollars. Call a licensed plumber when more than one fixture backs up at the same time, you see or smell sewage, water comes up the lowest drains when you run another, or a hand snake won't reach or clear the clog — these point to a main sewer line or vent problem that needs a power auger, hydro-jetting, or a camera inspection. Recurring clogs in the same spot also warrant a pro to check for pipe damage, a bellied pipe, or root intrusion. Don't climb onto the roof to clear a vent yourself — leave roof-height work to a pro.

Tools & parts

Cup plunger (sink/tub) — not a flange toilet plunger
Bucket and rags
Channel-lock / slip-joint pliers
Plastic hair-clog tool ('zip-it')
Hand drain auger (snake), 1/4-inch
Rubber gloves and eye protection
Old toothbrush or rag for cleaning the trap
Dish soap

Keep a record of every fix you make — what broke, what it cost, how you solved it.

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Based on: reputable DIY references (This Old House, Family Handyman, Bob Vila in spirit); plumbing fixture and drain manufacturer guidance; general residential plumbing code norms (drain/waste/vent principles)

This is general home-maintenance guidance, not professional plumbing advice. Conditions vary by home, pipe age, and local code. If you're unsure, smell sewage, see widespread backups, or have already used chemical drain cleaner, stop and call a licensed plumber.