How to Properly Install a Double Kitchen Sink Drain with an Air Admittance Valve (AAV)
- Mike Smith
- May 30
- 4 min read
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A poorly installed kitchen sink drain can lead to slow drainage, water backing up into the opposite sink bowl, and frustrating gurgling noises. In this project, I replaced an incorrectly installed double kitchen sink drain that used a double tee fitting and rebuilt it using a proper wye fitting, P-trap assembly, and air admittance valve (AAV), commonly known as a cheater vent.
If your kitchen sink is draining poorly or water rises into the other sink bowl, this repair may solve the problem.
Why Water Was Backing Up Into the Other Side of the Sink
The original installation used a double tee fitting on the horizontal drain section. When water drained from one side of the sink, it was forced toward the opposite bowl instead of flowing smoothly toward the drain line.
This caused:
Water backing up into the second sink bowl
Poor drainage performance
Potential gurgling noises
Increased risk of future clogs
For homeowners who use one sink bowl for drying dishes, this can quickly become an annoying problem.
The Problem With the Existing Cheater Vent
The kitchen sink was vented using an air admittance valve (AAV). While AAVs are commonly used when traditional venting isn't available, this one was installed very low under the sink cabinet. The AAV was also no an approved vent. You should always use a certified approved automatic air vent
Why AAV Height Matters
I always try to install an air admittance valve as high as possible beneath the sink.
Mounting the valve higher helps:
Reduce exposure to grease and debris
Improve long-term reliability
Keep moisture away from the valve gasket
Maintain proper airflow to the drain system
Removing the Old Drain Assembly
The first step was removing the existing drain assembly while leaving enough pipe for reconnection.
Once the old piping was removed, I began laying out the new drain system using:
A wye fitting
A 90-degree elbow
Trap adapters
1-1/2 inch ABS pipe
A union P-trap
An elevated AAV connection
Dry fitting the entire assembly before gluing ensures accurate measurements and proper alignment.
Measuring ABS Pipe Correctly
Accurate measurements are critical when building a kitchen sink drain assembly.
Measuring Hub to Hub
When measuring between fittings, measure from hub to hub.
For 1-1/2 inch ABS pipe, remember to account for the insertion depth of the pipe inside each fitting. This allows the final assembly to fit properly once glued together. For 1-1/2" pipe you will add 1-1/2" to the hub to hub measurement.
Establishing Trap Height
A temporary piece of pipe installed on the trap arm helps determine the correct vertical measurement to the P-trap.
This step makes it easier to locate the wye fitting and align the entire drain assembly before solvent welding.
Why I Installed a Wye Fitting Instead of a Double Tee
A wye fitting provides a much smoother path for wastewater than a double tee fitting.
Benefits of a Wye Fitting
Better drainage performance
Reduced turbulence
Less chance of water crossing into the opposite sink bowl
Easier maintenance
The wye directs water naturally toward the main drain instead of allowing it to collide inside the fitting.
Adding a Cleanout for Future Drain Cleaning
Kitchen sinks are notorious for grease and food-related drain blockages.
For that reason, I installed a cleanout on the end of the wye fitting.
Having a cleanout makes future drain cleaning much easier because an auger can be inserted directly into the drain system without dismantling the sink plumbing.
Solvent Welding the ABS Fittings
After confirming all measurements, the fittings were glued together using ABS solvent cement.
A Simple Tip for Better Glue Joints
When inserting a pipe into a fitting, I slightly rotate the fitting as it seats.
This helps spread the solvent cement evenly around the entire joint and promotes a complete seal.
Installing the Union P-Trap
Once the drain assembly was glued together, the P-trap was installed.
Some plumbers dislike union-style P-traps, but I have used them for years without issues when installed correctly.
Common Cause of P-Trap Leaks
Many trap leaks occur because the assembly is forced into position.
If the union nuts are difficult to thread on, the drain assembly is usually out of alignment.
Loosening the trap adapters at the basket strainers allows slight movement so the trap can align naturally before tightening.
The Finished Kitchen Sink Drain Installation
After completing the installation, water drained properly from both sink bowls without backing up into the opposite side.
The finished system included:
Properly positioned air admittance valve
Wye fitting for improved flow
Accessible cleanout connection
Correctly aligned P-trap
Improved overall drainage performance
This setup should provide reliable service while making future maintenance much easier.
Frequently Asked Questions
Why does water come up in the other side of my kitchen sink?
This is often caused by an improperly installed drain system, a partial blockage, or inadequate venting. A double tee fitting can sometimes contribute to this problem.
What is a cheater vent?
A cheater vent is another name for an air admittance valve (AAV). It allows air into the plumbing system without requiring a traditional vent pipe through the roof.
How high should an AAV be installed?
Most plumbers install an AAV as high as practical beneath the sink cabinet while keeping it accessible for replacement.
Is a wye fitting better than a double tee for kitchen sink drains?
Yes. A wye fitting provides smoother drainage and reduces the chance of water crossing into the opposite sink bowl.
Why add a cleanout under a kitchen sink?
A cleanout makes future drain cleaning easier by providing direct access to the drain line without disassembling the plumbing.
Do union P-traps leak?
When properly aligned and tightened, union P-traps are reliable and provide convenient access for maintenance and cleaning.
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As an Amazon Affiliate I reciece commision on purchases
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