Quick Answer:
If the sink drains slower right after installing a new garbage disposal, the most likely causes are a misaligned discharge elbow that creates an uphill run, a sagging accordion-style connector that traps water, or a partial blockage introduced during installation. Before calling a plumber, confirm the disposal’s discharge elbow points toward the trap arm with no uphill run, check the shape of any flexible connectors, and run a full sink of water to time how quickly it clears compared with faucet-only flow. If those checks don’t fix it, call a professional.
Why This Happens
New disposals change the piping layout under the sink. Small changes in angle or length of pipe can create low spots where water slows or pools. Common problems after installation include:
- An elbow rotated so the discharge is aiming uphill or into the wrong plane, forcing water to climb instead of flowing to the trap.
- A corrugated or accordion-style connector that sags and traps food or water instead of allowing a smooth fall to the P-trap.
- A misplaced or pinched pipe, loose clamp, or leftover debris from the installation that narrows the flow.
If you see visible moisture or new drips, also check the disposal and nearby joints — that can be related and is worth addressing. For related problems, see Leaks after installing new disposal for leak-focused checks and remediation steps.
Step-by-Step What to Do
1. Turn power off and visually inspect the hookup
- Unplug the disposal or switch the circuit breaker off before working below the sink.
- Look at the disposal discharge elbow and the pipe leading to the P-trap. The discharge elbow should point toward the trap arm without any uphill run.
2. Check for a sagging accordion-style connector
- If the connection between the disposal and trap is a flexible corrugated tube, feel for sagging or deep corrugations that hold water. These often trap food particles and slow drainage.
- If you have a corrugated connector, replace it with a smooth-walled trap adapter if you can do so safely, or have a plumber swap it out.
3. Run a full sink of water and time the drain
- Fill the sink basin completely, then remove the stopper and time how long it takes to empty. Repeat for the other bowl if you have a double sink.
- Now run the faucet only (no full fill) and compare the flow time. If an empty faucet drains much faster than a full sink, the issue is geometry or trapping under the sink rather than the disposal motor.
4. Look for other visible restrictions
- Inspect all clamps and slip-nuts for proper alignment and tightness. A misaligned trap arm can create a partial blockage.
- Check for debris around the sink flange and in the disposal throat (only when power is off and the unit is disconnected).
5. Reposition simple fittings if possible
- If the elbow is slightly rotated creating a shallow uphill run, you may be able to loosen the slip joint and rotate it a small amount to restore proper downhill slope.
- If repositioning requires cutting or major rework, stop and call a professional rather than forcing a makeshift fix.
What Not to Do
- Don’t “fix” slow draining by removing the trap or leaving it loose — trap water is critical to block sewer gas and maintain proper drainage.
- Don’t stick your hand into the disposal unless the unit is completely disconnected from power and you understand the safe procedure.
- Don’t force fittings into alignment that create an uphill run; if you can’t eliminate an uphill run or forced alignment, a plumber is appropriate to re-pipe correctly.
When to Call a Professional
Call a plumber if:
- You cannot eliminate an uphill run or forced alignment without cutting and re-piping.
- The drain is still slow after checking the elbow, replacing a sagging connector, and clearing visible debris.
- You notice persistent bad smells, repeated backups, or visible leaks. If the sink is backing up or the other fixtures are affected, it’s time to call a pro — for example, when a Sink backs up after disposal install the issue often needs professional attention.
Safety Notes
- Always disconnect power before working on or under the disposal.
- Never put your hand inside the disposal with power connected. Use tools (pliers, tongs) and remove debris with the unit powered off and unplugged.
- Wear gloves and eye protection when handling plumbing parts or when cleaning trapped food.
Common Homeowner Questions
- Why did it drain fine before and not now? — Small changes in pipe angle or a new flexible connector often create low spots that trap water after installation.
- Can I fix an uphill run myself? — Only if it’s a minor rotation of a slip joint; significant changes or cutting pipe should be left to a plumber.
- How long should a sink take to drain? — A full sink should empty in a minute or two; much longer suggests a restriction under the sink or in the trap.