Under kitchen-sink disposal erratic plumbing

tk3000 said:

Hello Folks,

About 14 years ago, I did install a disposal under a double-sink that lacked a disposal. Looking back, under the kitchen-sink, it likely is not compliant with code. Below is a pic:

View attachment 33593

The p-trap height seems to be ok. The 90d elbow used to connect the disposal discharge port to the pipe contraption probably is not ok. It has worked well for all those years though…


Most install seems to use a straight pipe out of the disposal discharge port. But, back then, it was easier to use what I had at hand; also, was also trying to optimize the useful storage space under the kitchen cabinet. The sharp sweep (short radius) of the 90d elbow connecting the disposal to the vertical pipe does not favor easy flow. Also, I am not sure if the cap is acceptable in this situation.

Any input on how to rectify that would be appreciated.

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opplumbinghubks said:

You should replace the sharp bend coming out of the disposal with a more gradual slope pipe, and swap out that T-joint with the cap for proper sink drain fittings. This will help prevent clogs and make everything flow better, while meeting proper plumbing standards. The rest of your setup with the P-trap looks fine.

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PJB12 said:

Hi TK3000,

The 90 degree turn on the disposer discharge fitting is by design. The manufacturers do this to help maintain some water below the plate while grinding so that the grind ring doesn't get hot & to be a lube so that pieces of bone don't lodge easily between the flails and the grind ring. It also has something to do with the knives, but I can't remember what they taught us. The slow draining below the grind plate also helps suspend the particles for easier washing out. But...

It is common practice for that turn-down to go into a 90 which is connected to a horizontal pipe that travels to a drain-tee compression fitting above a p-trap. The p-trap is directly under the other bowl. This lets the water slow down, but still suspend the solids. If the horizontal was too sort, junk could be shot up into the other bowl. That's why the trap is under the bowl without the disposer (to give length for the disposer discharge to lose force & slow down).

Pretty much, you'd shove what you have to the left, extending the pipe from your #2 fitting to the other side where the p-trap now lives.

Regarding the tee with a cap on top, maybe flip it up and use a wye for easy snaking both ways with a sink gun. (Optional)

If you don't mind a couple of hints that you probably already know:
A) Run the water for several seconds after the grind cycle to ensure solids are flushed from the trap. (They may solidify in the trap later.)
B) No stringy stuff is allowed, such as celery. It does evil things to disposers.

Paul

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PJB12 said:

HI TK3000,
I apologize but I can't view the attachment on my Genuine Mattel Barbie & Ken Anniversary Edition Computer. I'm trying to visualize what you propose, but can't.

You mentioned that the trap under the left bowl will be in the way. (Always are, aren't they?). It's difficult to make room for everything, especially with a disposer in the way. My solution at home is that I made a drawer with really short sides & put rails at the bottom of the cabinet. Instead of reaching around stuff, I pull the drawer forward.

Does it help to have the trap between bowls? You might then be able to use two wye fittings or long sweep tees. One is for each bowl. The disposer would be the one closest to the drain pipe in the wall.

Sometimes people will put a double wye with a cleanout plug on the end (more like a short cross). One bowl goes into each branch of the wye. The end of the wye goes to a horizontal for the trap. The problem is that if the drain in the wall can't handle what the disposer is sending quickly enough water may back up into the other bowl. And, some jurisdictions prohibit this (for the backing up reason), but your house = your decision.

Don't use two traps into a common double wye as some people do. When either bowl empties quickly, the vacuum can siphon the other trap dry.

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tk3000 said:

Hello Folks,

About 14 years ago, I did install a disposal under a double-sink that lacked a disposal. Looking back, under the kitchen-sink, it likely is not compliant with code. Below is a pic:

View attachment 33593

The p-trap height seems to be ok. The 90d elbow used to connect the disposal discharge port to the pipe contraption probably is not ok. It has worked well for all those years though…


Most install seems to use a straight pipe out of the disposal discharge port. But, back then, it was easier to use what I had at hand; also, was also trying to optimize the useful storage space under the kitchen cabinet. The sharp sweep (short radius) of the 90d elbow connecting the disposal to the vertical pipe does not favor easy flow. Also, I am not sure if the cap is acceptable in this situation and Plumber pricing for urgent repairs.

Any input on how to rectify that would be appreciated.

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nobes said:

Help! I need some plumbing advice. 2 weeks ago our kitchen sink filled up with dishwasher water and wouldn't go down. After plunging (did not work, and broke the seal of the plug) and removing the pipes under the sink and putting a 6ft snake/spring (no blockage found) it was draining again. Then a few days a go it filled up again, not with dishwasher water, along with the downstairs toilet sink. I released the pipes and it drained again. Everything was working again until this morning and both sinks were not draining. Released the pipe below the bathroom sink and they both drained (no blockage). Any ideas how to fix it?
Moved into the house 3 years ago, redone kitchen in February (not much change to pipe work, done by brother in law) only just start having this problem. Advice gratefully received!

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tk3000 said:

At first, I had the impression that your plumbing vent is clogged or blocked somehow.

Usually, the vent stack for the plumbing venting goes outside – typically through the roof. Dust and debris can clog the vent stack (especially if it is not capped). New houses may not have a plumbing venting stack going outside, but instead something called “Air Admittance Valve”. How old is your house? The air admittance valve looks like the following:



View attachment 33729

Edit: Even with the use of "air admittance valves" a house still would still require one plumbing venting pipe going to the roof. The deployment of "air admittance vales" would simply the DWV (Drain-Waste-Vent) system though (simplify = less labor + less material = cheaper).

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tk3000 said:

Hi Paul,

Sorry, it was my bad. Or something went awry with my post (I posted the pic in the wrong spot, but then few seconds afterwards I edited the pic (and previewed it) in the right spot. But, for whatever reason (some glitch), the post did not reflect it. Below is the pic:

View attachment 33727


A trap between the bowls could work. But, I am not sure how to go about it with “slip joint” plumbing. PVC has more variety of fittings, etc. I used PVC for p-traps in a bathroom in the past. But, I don’t know much about the possible fittings when it comes to slip-joint (my plumbing know-how is kind of limited in many ways).

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Ron Van said:

View attachment 33730

Eliminating the tee at B and making C a long sweep would be good but the biggest problem I see is after the P Trap. It looks like after the trap there is an elbow and then the drain goes straight down through the floor. In effect, you have no vent which means you are in danger of setting up a siphon and sucking the water out of your trap. It’s called a S Trap situation and is fairly common in older homes…but not to current codes and probably not to code when it was plumbed. There are several ways to fix it which have been discussed recently on this forum.

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Ron Van said:

View attachment 33730

Eliminating the tee at B and making C a long sweep would be good but the biggest problem I see is after the P Trap. It looks like after the trap there is an elbow and then the drain goes straight down through the floor. In effect, you have no vent which means you are in danger of setting up a siphon and sucking the water out of your trap. It’s called a S Trap situation and is fairly common in older homes…but not to current codes and probably not to code when it was plumbed. There are several ways to fix it which have been discussed recently on this forum.

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tk3000 said:

That condo was built in 1974. Was it likely allowed by code back then?

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tk3000 said:

Having said that, I never had any issue with it (bads odors, clogging; always worked flawlessly)

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PJB12 said:

I suppose the bottom line is: "Your House, Your Rules".
No problems in all of these years indicates a safely functioning drain. In a daily use room like a kitchen, you'll know quickly if the trap ever loses its seal.

At worst, when you sell the buyer's home inspector might be bright enough to catch it, but I doubt it very much. Yours is not obviously outside of the rather obscure code reference.

No loss of sleep necessary!

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dsteinhorn said:

How about an air admittance valve/vent installed in a T after the trap? Doesn't part of the issue relate to where the vertical pipe below the floor joins a vented drain pipe?

I see studs on the back wall and suspect one could even get the air admittance valve high up in relation to the level of the sink.

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PJB12 said:

With respect to you for thinking of an auto vent, I think I'd be inclined to skip it.
Since the drain gives you no problems, a mechanical vent could cause problems. (They are also kind of noisy sometimes in a pesky, groaning kind of way.)

Two problems with adding a mechanical vent quickly come to mind-
A) If the drain past the vent clogs or even slows, particles from the disposer waste can lodge under the diaphragm and allow sewer gas to escape into the room. (There was one in my house when I bought it. The disposer sent water with enough force to do exactly that on a regular basis- even with a clear 2" drain pipe. The laundry one was even worse.)

B) In many jurisdictions (like here), the diaphragm of the vent has to be above the flood rim of the vessel. That's again so particles or soap film build up from suds or backwash can't prevent a good seal for the diaphragm. Look at one in the store and you'll see how gentle the spring is that holds the very flexible and thin diaphragm is.



And, everywhere that I know of the vent has to remain "readily accessible".
Thus, you can't use your idea of putting it high in a stud bay unless there is an unattractive removable cover on the wall.

Additionally, the stud bay has to have a supply of air for when the vent is in "vacuum" mode. I've noticed them in commercial restroom walls behind grates that look like return air vents for furnaces.

If you ever go in a barber shop or beauty salon that has rows of sinks in the middle of the room, you'll often see a rather thick box looking backsplash along the back of the sink cabinet's deck. The mechanical vent is in there and the air supply is from a gap under the cabinet door.

Want a bigger project?
You mentioned the stud bay is open. Is there any chance that you can drop a pipe down from the attic into that bay and tie in as a vent? The attic end of the pipe will tie to your existing VTR pipe. It may not be 100% sized to code, but will work well.

Wish I had a simple solution to offer,
Paul

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