Quick Answer:
If your sink drains slower after adding a disposal, stop using the unit and check the plumbing connections and trap alignment first. Slow drainage often comes from a misaligned trap, a loose disposal inlet, or a grease build-up farther down the line. Quick checks and simple cleaning can fix most problems; call a pro if the drain stays slow after basic troubleshooting.
Why This Happens
Adding a garbage disposal changes the shape and flow of your drain system. Common causes of worsened drainage after installation include:
- Misaligned or loose connections where the disposal meets the sink or drain pipe, which can create partial blockages.
- A P-trap that was shifted, pinched, or reinstalled at the wrong angle during the job, slowing flow.
- Grease or food debris that was dislodged during installation and pushed farther into the drain pipe. See Grease clogging kitchen drain for more about how grease behaves in drains.
- An existing partial clog that was unnoticed until the disposal changed flow patterns, causing the sink to now back up sooner or more often. If you notice both sinks affected or intermittent backups, this can look like the problem in Kitchen sink drains slow then backs up.
Step-by-Step What to Do
1. Stop using the disposal and run water briefly
- Turn the disposal off and run cold water for 10–20 seconds to clear loose debris. Don’t use the unit while you inspect plumbing.
2. Check for obvious clogs at the sink and flange
- Remove any visible food scraps around the sink flange and inside the disposal mouth with tongs or pliers—never your hand.
3. Inspect disposal connections and trap alignment
- Look under the sink where the disposal connects to the drain pipe and P-trap. Make sure all slip nuts are snug but not overtightened.
- Confirm the discharge elbow from the disposal lines up cleanly with the trap inlet. If the trap is forced into a sharp angle, water will drain slowly.
- If the trap is misaligned, loosen the slip nuts, reposition the trap so it sits straight, and retighten. Check for leaks after you run water.
4. Remove and clean the P-trap if needed
- Place a bucket under the trap, loosen the slip nuts, and remove the trap. Clear any clogs or grease, then reinstall, ensuring correct alignment.
- This is a common place for food and grease to collect after an install.
5. Test the line beyond the trap
- If the trap is clear but the sink still drains slowly, use a hand auger (plumbers’ snake) into the trap arm or the disposal discharge to clear further clogs.
- A short manual snake often reaches common trouble spots without damaging pipes.
6. Run a final flush
- Run cold water for a full minute while briefly turning on the disposal to rinse remaining debris through the system.
What Not to Do
- Do not install disposals without checking slope.
- Do not reach into the disposal with your hand. Always disconnect power first and use tools.
- Do not pour strong chemical drain cleaners into a disposal—chemicals can damage components and pipes and are often ineffective on grease inside disposals.
- Do not run the disposal without water or try to force a jammed impeller by turning the unit on; use the manual reset and hex key method per the manufacturer.
When to Call a Professional
- There is persistent slow drainage or backups after you’ve checked and cleaned the trap and connections.
- Leaks appear at pipe joints you can’t fix or the disposal’s mounting assembly looks damaged or loose.
- You suspect a clog deep in the household drain or sewer line (multiple drains affected, gurgling sounds, or repeated backups).
- If you’re uncomfortable working under the sink or with electrical components on the disposal, call a plumber or appliance technician.
Safety Notes
- Always disconnect power to the disposal before working on it—unplug it or switch off the circuit at the panel.
- Never put your hand into the disposal. Use tools (tongs, pliers) to remove debris and a hex key for manual rotor turning if provided by the manufacturer.
- Wear gloves and eye protection when removing the P-trap; water and debris can spill.
- If you use a hand auger, use one designed for sink drains and follow tool safety instructions. Avoid harsh chemicals.
Common Homeowner Questions
- Why did the drain get worse after installation? — A misaligned trap or a connection that pushed debris into the line is the most common cause.
- Can I fix it myself? — Yes, if the problem is at the trap or a loose connection; stop and call a pro for persistent or deep clogs.
- Will grease cause this right away? — Grease may cause slow drainage over time or be pushed deeper during installation; cleaning the trap and nearby pipe often helps.