You are here:

Plumbing in the Home/kitchen sink doesnt drain unless disposal on



My kitchen sink fills with water unless the disposal is turned on. Then no matter how much water is in the sink, it does drain, but not fully as I can see the water about an inch on top of the disposal's intake. The disposal works and sounds normal.  There is a dishwasher attached to a vent on the sink, and a cold water tap.

A month ago, the basement sewer line were cleared of a blockage after the utility sink. I thought this time it might be blockage from having coffee grinds dumped in, so I removed and cleaned the P trap under the kitchen sink, and as much of the lateral pipe going into the wall as I could see. There was lots of grease and the pipes were lined with a layer of harden grease.  Now putting water into the disposal without the P trap underneath shows water draining out as fast as its put in.  I would think that the disposal is therefore ok.

Unfortunately, after re-assembly, the original problem persists, so I am wondering if I didnt clean the pipes deeply enough or maybe the debris is just pushed downstream after I dislodged it, or maybe some vent somewhere is blocked.

I think the spot you missed is in a part called a "baffle tee".  In the drain pipes between the disposer and the other sink bay there is a tee fitting. Inside this tee is a baffle to divert water from the disposer down the pipe rather than having it go up into the other sink bay.

Because of this baffle, the actual opening is pretty small and easily clogged. Remember, this side gets the ground up debris from the disposer. I think if you take the tee out and clean it your problem will be solved.

Good Luck,

---------- FOLLOW-UP ----------


Thanks for your prompt reply. Im not sure where this "t" and what "the other sink bay" is.   

I have only a single sink with a Insinkerator disposal and a dishwasher attached with a air gap mounted on the lip of the sink between the discharge hose from the dishwasher and then to a hole on the disposal.  I think this air gap is to allow drainage from the dishwasher into the sink. While there were some debris inside the air gap, it seems to drain ok in reverse when I took it off the sink and took off the hose from the dishwasher. The heavy black hose from the disposal to the air gap also seems to drain as I put water into the sink. (I couldnt take off the black heavy hose -both ends can rotate but its really tight on and I couldnt pull it off, and I didnt think I should cut it off as then it might be too short.)

Is this the t you mean?  If so its not likely the problem as the situation has not changed after the above. Is there a vent or t further along inside the wall after the lateral pipe going into the wall?

Before I put up this question/post, I had used a wire hanger to clean out the lateral pipe to its connection to apparently a down pipe, and then flushed 20 gals of very hot water with detergent already.  I could feel the pipe that drains this sink get hot all the way down to the basement floor, so I thought there is nothing blocking the drain anymore.

Sorry, I miss-read your question and assumed you had the typical double-bay sink setup.

There may be some kind of debris that is not water soluble clogging the disposer.  Have you looked inside with a flashlight?  Fibrous materials can catch on the blades around the sides of the grinding chamber and not be flushed out.
The drain elbow can also be removed pretty easily for a look inside that area to see if there are any obstructions to drainage.  Past that, I can not think of any reason it will not drain.

---------- FOLLOW-UP ----------

Thanks for your attention to this. I took off the trap again, ran water thru the Insinkerator disposal, and that was not blocking at all. I filled up the lateral pipe with water slowly and after 2 cups indeed it is blocked.  (I dont understand why turning on the disposal clears the sink, but maybe its just enough pressure to get it pass a blockage.) So it seems  its not the disposal.
I ran a snake into the lateral pipe - about 15", then a 90 degree bend then about a 1' horizontal section to where it might go into another pipe, which I presume is attached to a vent. I couldnt get the handheld simple snake to go any further, even after pushing, shoving and twisting all I could. Then,
I ran a long 20' piece of bamboo down the vent pipe that is just where it should be, pass the likely junction, about 10' down, until it hit something , hopefully a bend.
BUT to no avail - after reassembly, the blockage is still the same. Rrrrrrrr!!

Hi Tom,
Sounds like it's time to call in a pro with some power equipment to do a proper job on this drain. Homeowner and hand powered snakes only punch a hole in a blockage and may give temporary relief.  It takes a professional level power snake with blades to really get the job done.
Good Luck,

Plumbing in the Home

All Answers

Answers by Expert:

Ask Experts


Dana Bostick


Pretty much any residential plumbing questions. For "item specific" details such as a specific model of fixture, I will need to research and there may not be any useful information available. Note: I live and work in Southern California. We do not, as a rule, use hot water or steam heating systems, oil fired boilers or private water wells so my knowledge in those areas is pretty limited. There are others here on AllExerts that can probably answer those questions better.


Retired, Licensed General Contractor with Plumbing license. Active Home Inspector, Litigation Consultant and Infrared Thermographer, Online Marketing specialist.

Publications "Rain Maker" as "Inspector Dana", about making money online.

30+ years in the building trades, Licensed General Contractor (Retired), Certified Infrared Thermographer Internet Entrepreneur, Amazon & eBay Merchant (deals-by-dana)

Awards and Honors
Listed FHA Fee Inspector, FHA 203(k)Consultant, HUD Mobile Home Inspector

Past/Present Clients
Home buyers, sellers and owners, Investors, Commercial roofing companies (infrared roof scans for moisture intrusion, Litigation Consulting for "Slumlord" laws in SoCal

©2017 All rights reserved.