Quick Answer:
If a sink is draining slowly and you suspect the trap was assembled wrong, start by visually comparing the trap under the sink to a normal P-trap. Look for extra bends, long drop depths, or offsets that make the water sit or flow poorly. Small corrections—replacing the trap with a standard P-trap shape or simplifying the inlet to the waste arm—often fix the problem. If you see odd pipe geometry, don’t assume a drain snake will fix it.
Why This Happens
Most kitchen and bathroom sinks expect a simple P-trap: a short curved section that holds water to block sewer gas, followed by a straight waste arm that leads into the wall or floor drain. When the trap is built with extra turns, a long tailpiece, or a deep drop before the waste arm, water can slow, mis-siphon, or leave solids sitting in low spots. You may notice the trap has multiple bends or an offset that changes flow direction.
Common layout problems to look for:
- a trap that drops straight down a long distance before bending toward the wall
- additional 90-degree fittings on the waste arm
- a reversed bend or extra U-shape that creates more than one trap point
These layouts can lead to standing water and slow drainage, and they’re why you’ll sometimes see issues like P-trap too deep causes clogging or a Trap offset causing backup on other fixtures.
Step-by-Step What to Do
Step 1 — Look before you touch
- Open the cabinet and clear things out so you can see the plumbing easily.
- Put a bucket under the trap in case there’s water in it.
Step 2 — Compare the trap to a standard P-trap
- A standard P-trap is a smooth curve (the “P” shape) with a short horizontal waste arm into the wall. Note whether your trap has extra bends, long vertical drops, or offsets before the waste arm.
- Mark or photograph the current layout so you can compare after any work.
Step 3 — Test the drain flow
- Run the tap and watch how quickly the sink empties. Listen for gurgling or bubbling in the sink or nearby fixtures—these signs point to poor trap geometry or a venting issue.
- If water pools in place and drains only slowly, that reinforces a geometry problem rather than a simple clog.
Step 4 — Remove and inspect the trap (if comfortable)
- With the bucket under the trap, loosen the slip nuts and take the trap apart to inspect for hair, grease, or foreign objects. Clean it out and look at how the pieces fit together.
- Compare the cleaned trap parts to how a P-trap should sit: one curved piece plus one straight waste arm into the wall. Note any extra fittings that force additional bends.
Step 5 — Simplify the layout or replace the trap
- If the trap assembly has unnecessary elbows or a long drop, replace it with a standard P-trap and a properly cut waste arm so the outlet is as straight and short as practical to the wall stub.
- Reassemble hand-tight, then test by running water and checking for leaks and improved drainage.
What Not to Do
- Do not assume snaking will solve a geometry problem if the trap layout is incorrect.
- Do not pour caustic chemical drain cleaners into standing water. They rarely fix geometry issues and can damage pipes and your skin.
- Do not force fittings or overtighten plastic slip nuts—stripped threads or cracked fittings will cause leaks.
- Do not cut or re-route pipes unless you are confident in measuring and joining plumbing; incorrect cuts can make the layout worse.
When to Call a Professional
- After you compare and simplify the trap but the drain is still slow or backs up into other fixtures.
- If you find multiple strange offsets or a trap that’s buried inside a boxed-in chase and can’t be made into a simple P-trap without rerouting.
- If you smell sewer gas, see persistent leaks, or discover corrosion or brittle waste piping—these are signs for a licensed plumber.
- If changes require cutting into walls, rerouting the waste line, or adjusting vents—these jobs are best handled by a pro.
Safety Notes
- Wear gloves and eye protection when working under sinks. Old trap water can contain bacteria and debris.
- Have a bucket and rags ready for spills. Work slowly when loosening slip nuts so water drains into the bucket.
- Avoid mixing chemical cleaners with mechanical cleaning. If chemicals were used previously, flush the trap carefully and ventilate the area before working.
- If you’re unsure about gas smells or major leaks, evacuate the area and call a professional immediately.
Common Homeowner Questions
- Why did the sink suddenly go slow? — A change in trap geometry, accumulated debris, or a partial clog in the waste arm can cause a sudden slowdown.
- Can I replace the trap myself? — Yes, replacing a visible trap with a standard P-trap is a common DIY job if you can access the fittings and have basic tools.
- Will a plumber just snake it out? — Not always. If the problem is poor trap layout or incorrect offsets, a plumber will likely reconfigure the trap rather than just snake it.