Symptoms
- Both basins drain slowly, not just one
- Slowness affects the sink whether the disposal is used or not
- Gurgling from one side while the other drains
- Problem has developed gradually
Likely causes
- CommonGrease and food buildup in the shared drain line past both basinsSince both basins funnel into the same line, buildup there slows drainage for the whole sink.
- CommonClog in the main trap under the sinkA single trap often serves both basins before the line continues toward the wall.
- PossiblePartially clogged garbage disposal outletCan slow the whole sink if it feeds into the shared line.
- Less commonVent or main line issue affecting the whole fixtureWorth considering if other fixtures are affected too.
What to do
- Stop pouring grease or oils down either side of the sink going forward.
- Try a baking soda and vinegar treatment down both basins, letting it sit 15 minutes before flushing with hot water.
- Plunge one basin at a time with the other covered by a wet rag for good suction.
- If still slow, remove and clean the shared P-trap under the sink, checking carefully for grease and food debris.
- Check the garbage disposal's outlet connection for buildup if the sink has one.
- For a persistent clog, use a hand-crank drain snake through the trap arm heading toward the wall.
- Run hot water in both basins after clearing to confirm improved drainage overall.
Tools and parts
- Plunger
- Adjustable pliers
- Baking soda
- Vinegar
- Hand-crank drain snake
When to call a pro
Call a plumber if cleaning the shared trap and snaking doesn't restore normal flow to both basins.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.