How To Repair a Kitchen Sink Drain Trap

A clean and functional kitchen sink helps ensure a healthy and efficient kitchen environment. If your sink drains slowly or emits unpleasant odors, you likely have issues with your drain trap. We will walk you through the steps to troubleshoot and repair your kitchen sink drain trap, guaranteeing smooth and hassle-free sink operation. In this segment, This Old House plumbing and heating expert Richard Trethewey demonstrates how to replumb a poorly draining sink.

*Cost data sources from Angi

Tools and Materials Needed to Repair a Kitchen Sink Drain Trap

Before beginning the repair process, gather the following tools and materials:

• New PVC trap and drainpipe
• Plumber’s tape
• PVC disposer elbow
• PVC pipe cutter
• PVC primer and cement
• PVC T-fitting
• Screwdriver
• Stainless steel hose clamps

Pro Tip: Richard Trethewey, This Old House plumbing and heating expert, advises: “The cardinal rule before starting any plumbing project: Turn off the water.” He also recommends always threading nuts by hand before tightening with a wrench or pliers, since copper and brass are soft metals and it’s easy to cross or strip threads and ruin the fitting.

Steps for Kitchen Sink Drain Trap Repair

Follow these four steps to repair your kitchen sink drain trap. 

Step 1: Remove the Old Trap and Drain Lines

1. Turn off the water supply to the sink.
2. Place a bucket underneath the sink to catch any water.
3. Remove the garbage disposer if present.
4. Disconnect all old traps and drain lines from beneath the sink.

Step 2: Prepare the Drainpipes

1. Use PVC primer and cement to glue a solid plug over the end of one drainpipe stub out.
2. Glue a threaded cleanout plug onto the end of another stub out.
3. Locate the dishwasher connection on the side of the garbage disposer.
4. Remove the knockout plug from the disposer using a screwdriver.
5. Reinstall the garbage disposer under the sink.

Step 3: Install the New Trap and Drainpipe

1. Attach a PVC disposer elbow to the garbage disposer.
2. Install a new PVC trap and drain pipe to the stub out in the wall.
3. Connect the disposer elbow to the new trap with a PVC T-fitting. 
4. If the fitting is too long, cut it to length with a PVC pipe cutter.

Step 4: Connect the Sink and Dishwasher

1. Attach the strainer and PVC tailpiece to the drain hole in the sink.
2. Hold the PVC waste arm in place, spanning from the tailpiece to the T-fitting on the garbage disposer.
3. Mark cut lines on the waste arm and tailpiece, then cut both with the PVC pipe cutter.
4. Install the waste arm and tighten the threaded fittings to connect it to the tailpiece and T-fitting.
5. Attach the dishwasher’s discharge hose to the disposer using two stainless steel hose clamps.
6. Tighten the clamps with a screwdriver.

Testing the Sink Drain Trap Repair

After completing the installation, we recommend testing your work by doing the following:

1. Turn on the kitchen faucet and let the water run.
2. Observe the sink to ensure it’s draining properly.
3. Check underneath the sink for any leaks.
4. Listen for any unusual sounds that might indicate improper installation.

If you notice any issues during testing, double-check your connections and make any necessary adjustments.

Maintaining Your Kitchen Sink Drain Trap

Regular maintenance will prevent future issues with your kitchen sink drain trap. Here are some tips to keep your drain trap in good condition:

• Avoid pouring grease or oil down the drain.
• Clean the trap periodically to remove buildup.
• Run hot water through the drain regularly to prevent clogs.
• Use a drain strainer to catch food particles.

Pro Tip: Richard Trethewey, This Old House plumbing and heating expert, cautions against quick fixes for loose drain joints: “Duct tape won’t solve this or any other plumbing problem. And I can almost guarantee that the day after you glue the joints together, somebody will lose a ring down there and you’ll have to cut the trap to retrieve it.” Instead, check whether your tailpiece or waste line is too short or too long — improper pipe lengths are a common cause of joints that won’t stay tight.

Troubleshooting Common Sink Drain Trap Issues

Foul odors, leaks, and more could signify problems with your kitchen sink drain trap. Here’s how to address these and other common issues:

Foul Odors

If you notice unpleasant smells coming from your sink, make sure the P-trap is properly filled with water. Clean the drain and P-trap to remove any buildup and check for proper venting of the plumbing system.

Leaking P-Trap

If you notice water leaking from the P-trap, check all connections and tighten them if necessary. Inspect the washers and replace them if they’re worn or damaged. If the trap itself is cracked, replace the entire unit.

Overflowing Dishwasher

An improper dishwasher connection can lead to water backing up into the sink, especially during drainage cycles. Make sure the dishwasher’s discharge hose is high-looped or properly air-gapped. Check connections for any kinks or obstructions. If problems persist, inspect the dishwasher’s internal filters and drain pumps.

Pro Tip: Richard, This Old House plumbing expert, explains why a high loop matters: “Any dishwasher manufacturer insists on one thing, a high loop. That means you run your hose to as high as you can get it right underneath your kitchen countertop height. So now two things happen when the pump shuts off, you now have a column of water strong enough to force its weight down and hold that check valve shut.”

Slow Draining

If your sink drains slowly, remove the P-trap and clean it thoroughly. If the issue persists, use a plumber’s snake to clear any clogs further down the drain line. Should the problem continue, consider calling a professional plumber.

This Old House plumbing and heating expert Richard Trethewey advises a measured approach: “Old house plumbing can be delicate. You don’t want to come in with guns blazing—blasting water down the drain or ramming the clog.” Start with a plunger and gently escalate the action as needed.

When To Call a Professional for Your Drain Trap Issues

If you encounter any of the following issues with your kitchen sink drain trap, it’s best to consult with a licensed plumber to avoid potential water damage or more severe plumbing problems:

• Complex plumbing configurations
• Damage to the main drain line
• Persistent leaks despite your repair attempts
• Recurring clogs or backups