Quick Answer:
A flood that shows up the same day as a repair usually means something under the sink was moved, misaligned or left partly blocked. Start by inspecting the drain connections, trap arm slope and any new vent device. If you can’t confirm proper alignment or the problem repeats after a full-basin dump, call the plumber who did the work or a licensed pro.
Why This Happens
When a repair changes the tailpiece, trap or drain alignment the outlet can end up with an uphill run, a kinked connection or a flexible accordion piece that holds water and debris. Partially blocked fittings, a misinstalled trap arm, or a newly added Air Admittance Valve (AAV) that’s loose can all allow a slow or sudden backup. If the issue started right after work, don’t assume it’s unrelated — installers sometimes make tight fits or shortcuts that lead to recurring backups. For similar causes after a trip, see Overflow after long vacation.
Step-by-Step What to Do
1. Clear the area and prepare
- Place towels and a bucket under the sink to catch water.
- Turn off the cabinet lights or keep a flashlight handy so you can see connections clearly.
2. Inspect under-sink connections
- Look at the tailpiece and trap. Check for an accordion-style flexible connector — these trap debris and are a common failure point. If you see one, note its location and condition.
- Check that compression nuts and slip joints are snug but not over-tightened. Look for signs of recent disturbance: fingerprints, fresh tool marks, or hand-tightened joints.
- Look for forced alignment — the tailpiece or trap should not be bent or twisted to meet the wall stub-out. Forced alignment often means the trap sits at an odd angle or the inlet and outlet aren’t lined up.
3. Confirm the trap arm slopes to the wall
- The trap arm (the horizontal run from the trap to the wall) should slope gently downward toward the wall. If it slopes up or is level for a long run, waste water can stall and back up into the sink.
- Feel along the trap arm for soft spots, low points where debris can collect, or any upward jog created when fittings were reinstalled.
4. Check any new AAV (air admittance valve)
- If a new AAV was installed during the repair, get close and sniff for sewer gas — a strong smell can mean the cap is loose or the valve is faulty. Also check that the valve is vertical and capped tightly according to the manufacturer’s orientation.
- Listen for hiss or air noise when running water; that can indicate an improperly seating AAV.
5. Retest using a full basin dump
- After you verify alignment and fittings, remove towels and buckets, then fill the basin completely and dump it in one go. A full-basin dump reproduces the volume a sink sees in normal use and will reveal whether the drain can handle the flow.
- Watch under the sink as the water moves. If it backs up immediately or shortly after dumping, note exactly where the water starts to appear and any noises from the trap or wall stub-out.
What Not to Do
- Don’t assume the repair is unrelated — misalignment and uphill runs create recurring backups and they commonly appear right after work is done.
- Don’t keep using the sink if you see active leaking or repeated backups; that risks water damage to cabinets and flooring.
- Don’t rely on small trickle tests. A slow drip won’t reveal flow problems that show up under a full load.
- Don’t attempt to “guess” the trap slope or fittings if you can’t verify them visually — if you can’t confirm proper slope and fittings, a plumber is appropriate.
When to Call a Professional
- If you find an accordion connector, forced alignment, or an uphill run you can’t fix yourself.
- If the AAV smells strongly of sewer gas or feels loose and you’re not confident reinstalling it.
- If the sink still backs up on a full-basin dump after you’ve checked connections and slope.
- If you notice active leaks, pooling water, or water damage to cabinets or floor materials.
- If you want the original installer to correct the work — ask them to come back and fix it before damage worsens; if they won’t, call a licensed plumber.
- For other timing-related overflow patterns, check guidance on Sink overflows only at night to compare symptoms.
Safety Notes
- Turn off the water supply to the sink if you need to loosen fittings or work on the trap.
- Avoid using harsh chemical drain cleaners under a sink with recent repairs; they can damage seals and are dangerous if mixed with other products.
- Watch for electrical devices and wiring inside the cabinet. Pull power at the breaker if water is near outlets or powered garbage disposals before working underneath.
- Wear gloves and eye protection when handling drain components, and use a bucket to control spills.
Common Homeowner Questions
- Why did the sink flood right after the plumber left? — Most likely a misaligned trap, an accordion connector, or a partially blocked fitting installed or disturbed during the repair.
- Can I just replace the accordion connector myself? — Yes if you’re comfortable with basic plumbing: shut off water, remove the old piece and install a rigid or smooth tailpiece and proper slip nuts. If not, call a plumber.
- Is a full-basin dump necessary for testing? — Yes. It recreates normal flow and will reveal backups that a light trickle won’t show.