Double kitchen sink slow draining after disposal trap installed.

[JSwift]

I have a dual kitchen sink with recently installed drain plumbing that is not draining slowly (pictures below). Prior to the new plumbing the AAV was about 10” above the top of the lateral line into the wall (where it goes to a 90° and into the slab). The disposal had no trap, it was a straight pipe into the tailpiece from the other basin which had a small baffle inside (I’m not sure if that style tailpiece has a specific name?). The owner added a trap to the disposal which leads to a long-turn wye followed by a sanitary tee which connects the AAV, then into the wall. The other sink basin leads from a short tailpiece into two 90° bends (owner said the lateral pipe was in the way and couldn’t align a straight tailpiece to the trap) then into the trap. Both sinks will fill to 1/4”-1/2” above the flange before beginning to drain and maintain that water height. The disposal with gurgle a little and air comes up. I was suspicious of the AAV at first so I removed it but nothing changed. The AAV is currently 4” above the top of the lateral line. It’s a Rectorseal Magic Vent.

What could be going on here? Has the new plumbing created an air lock somewhere? Or does the disposal discharge need an AAV before entering the wye? Any help is greatly appreciated! Thank you all!

 

[Reach4]

You have a probably have clog in the wall or farther. Get you pipes snaked.

What is the timing of this? Did your lines clog right after the new work was done, but did not clog before the new work was done? I suspect not, but you can tell us.

There is a problem that is not venting. Where the pipe in the wall turns from vertical to horizontal is a common place for a clog.

Here is a test. Let the water slowly drain out overnight. Then pour water fairly slowly from a 5 gallon bucket into the right bowl while watching for the water to rise in the bottom of of the disposal (spread the flaps and use a flashlight if necessary). How much water do you pour before the water in the disposal rises? You can measure that with a ruler (water level before and after pouring) or weighing the bucket before and after pouring. With that, we can estimate how far down the line the clog is.

I am not a plumber.

 

[Sponsor]

 

[WorthFlorida]

If the slow drain started after the trap was installed for the disposal, the disposal connection without a trap was working as a vent. Now you say you hear a little gurgle from the disposal (probably from the trap). Because the main drain appears to have a clog, air in the pipe (positive pressure) before the clog has nowhere to go without another roof vent before the clog so the air gets pushed back by the slow draining water.

AAV's are an air check valve, that is air is only allowed into the drain pipe (negative pressure) as water drains to prevent the trap from being siphoned dry. When taking off the AAV and there was no changed with the draining seems to prove as Reach suggest, a clog further down.

 

[Reach4]

AAV's are an air check valve, that is air is only allowed into the drain pipe (negative pressure) as water drains to prevent the trap from being siphoned dry. When taking off the AAV and there was no changed with the draining seems to prove as Reach suggest, a clog further down.

Worthwhile test, but if that helps, there is still a second problem downstream.

 

[JSwift]

You have a probably have clog in the wall or farther. Get you pipes snaked.

What is the timing of this? Did your lines clog right after the new work was done, but did not clog before the new work was done? I suspect not, but you can tell us.

There is a problem that is not venting. Where the pipe in the wall turns from vertical to horizontal is a common place for a clog.

Here is a test. Let the water slowly drain out overnight. Then pour water fairly slowly from a 5 gallon bucket into the right bowl while watching for the water to rise in the bottom of of the disposal (spread the flaps and use a flashlight if necessary). How much water do you pour before the water in the disposal rises? You can measure that with a ruler (water level before and after pouring) or weighing the bucket before and after pouring. With that, we can estimate how far down the line the clog is.

I am not a plumber.

before the work was done the lines didn’t appear to drain slow but maybe they did and it just wasn’t slow enough to be very obvious. After the new plumbing it is very obvious. I tried the bucket filling method and also let the faucet run on the sink side for 15 minutes and no water backed up into the disposal side during either test. I did notice that when I filled the sink and then removed the plug allowing the water to drain the AAV made a vibrating sound which I assume is just the valve operating as it should.

 

[Reach4]

before the work was done the lines didn’t appear to drain slow but maybe they did and it just wasn’t slow enough to be very obvious. After the new plumbing it is very obvious. I tried the bucket filling method and also let the faucet run on the sink side for 15 minutes and no water backed up into the disposal side during either test. I did notice that when I filled the sink and then removed the plug allowing the water to drain the AAV made a vibrating sound which I assume is just the valve operating as it should.

A belly in the drain line down the line could explain your symptom I think.

If the test that WorthFlorida proposes lets the draining happen without problem, I would think that would be the problem.

 

[WorthFlorida]

I think Reach is right, the main has a belly in it. Nothing appears on the new work side to have slowed things down. How old is the home and is the main to the street, clay, cast iron or PVC? Any trees roots possible? To be sure of a belly only a camera can tell for sure. Do any other drains, sinks, etc., show any problems draining?

 

[JSwift]

I think Reach is right, the main has a belly in it. Nothing appears on the new work side to have slowed things down. How old is the home and is the main to the street, clay, cast iron or PVC? Any trees roots possible? To be sure of a belly only a camera can tell for sure. Do any other drains, sinks, etc., show any problems draining?

The home was build in 2005. The main to the street is PVC and according to the drawings from the local sewer company there aren’t any lines near the trees. Oddly no other sinks/shower/tub seems to have any problem draining.

I'm going to try the test you mentioned tomorrow morning and see what happens. You mean remove the disposal trap and go back to a straight pipe, correct? If it drains well without the disposal trap would that be more evidence of a belly or something else? Assuming no change I’ll snake the drain as well and report back.

 

[JSwift]

A belly in the drain line down the line could explain your symptom I think.

If the test that WorthFlorida proposes lets the draining happen without problem, I would think that would be the problem.

Thank you for the drawing! I was a little confused at first. I’ll be trying WorthFlorida’s method tomorrow as well as snaking the drain. Hopefully rule something out or fix it.