A double kitchen sink is one of those modern conveniences that makes daily life easier—until it starts backing up. Few things are more frustrating than running water down one side of the sink, only to see it bubble up in the other. Not only is it inconvenient, but it’s also a sign that something is wrong in your plumbing system.
So, what causes this problem? Let’s break it down.
Common Reasons for a Double Sink Backup
1. Clogged Drain Line
The most common culprit is a clog in the shared drain line. When one side of the sink is blocked, water has nowhere to go and is forced back up into the other basin.
- Grease, food scraps, and soap scum are typical offenders.
- Over time, these build up and narrow the drain pipe, leading to backups.
2. Garbage Disposal Issues
If your sink has a garbage disposal, it may be contributing to the problem.
- A jammed or poorly installed disposal can block water flow.
- Incorrect installation of the disposal or drain pipes may cause cross-backup between the two basins.
3. Vent Pipe Blockage
Plumbing systems rely on vent pipes to balance air pressure and allow wastewater to flow smoothly. If the vent pipe is blocked—by debris, leaves, or even a bird’s nest—it can cause slow drainage and backups in the sink.
4. Improper Drain Design
Sometimes, the issue is in the way the plumbing was set up. If the P-traps or pipes under the sink were installed incorrectly, it may lead to water backing up from one side to the other.
Can You Fix It Yourself?
Some minor backups can be cleared without professional help:
- Try hot water and dish soap to break down grease clogs.
- Use a plunger (one designed for sinks, not toilets) to loosen a blockage.
- Check your garbage disposal to ensure it’s clear and running properly.
⚠️ Avoid harsh chemical drain cleaners. ⚠️ They can damage your pipes and often provide only a temporary fix. ⚠️
When to Call a Plumber
If DIY fixes don’t solve the problem—or if the backup keeps coming back—it’s time to bring in a professional. A licensed plumber can:
- Use specialized tools like augers or hydro-jetting to clear tough clogs.
- Inspect the vent system and drain design.
- Ensure your garbage disposal and piping are installed correctly.
Preventing Future Sink Backups
- Scrape plates into the trash before rinsing.
- Dispose of grease properly instead of pouring it down the drain.
- Run cold water when using your garbage disposal to keep debris moving.
- Schedule routine drain cleaning to stop buildup before it becomes a problem.
Keep Your Kitchen Running Smoothly
A double sink backing up into itself isn’t just annoying—it’s a red flag that something is wrong with your plumbing system. Tackling the issue early can save you from bigger (and messier) problems later.
If you’re in the Seattle area and struggling with sink backups, Fischer Plumbing is here to help. Our experienced plumbers can diagnose the problem and get your kitchen back to normal quickly.
