Garbage Disposer Code Question

Jdoll42 · Feb 26, 2008

I recently (about 8 months ago) had a "final plumbing" inspection on my house. The plumber did all of the rough in, and I did all of the finishing (installing faucets, sink traps, toilets, etc.) I got dinged by the inspector because I had my dishwasher drain hose hooked to my garbage disposer. He said that was against code and attributed it to centripetal force pushing waste back down the dishwasher hose. I thought all dishwashers had a check valve to prevent this, but even without, why would garbage disposers have a port to hook up the dishwasher if it causes problems? Just thought I'd run it by you guys and see what light you could shed on the issue. Anybody else heard of this?

Patrick88 · Feb 26, 2008

You might need to install an air gap. Knowing the location you live in will help anybody that knows your code can help you.

Sponsor · 2022-01-29T12:20:58-0800

Jdoll42 · Feb 26, 2008

patrick88 said:
You might need to install an air gap. Knowing the location you live in will help anybody that knows your code can help you.

What I did to pass the inspection is to hook the dishwasher discharge up to the tailpipe on the other sink bowl. That's how the inspector wanted it anyway. For reference, I'm in rural Madison County, IL (just across from St. Louis, MO.)

MG · Feb 26, 2008

I live in Madison county and been in lots of new construction homes there. I can't recall seeing any airgaps installed.

Jdoll42 · Feb 26, 2008

MG said:
I live in Madison county and been in lots of new construction homes there. I can't recall seeing any airgaps installed.

Yeah, they don't require an air gap in the dishwasher discharge line, but you sure as heck can't run it into your garbage disposer. Seems odd to me...

SteveW · Feb 26, 2008

As a non-pro, I think that if you don't use an air gap, you are required to do a "high loop" of the DW drain line before it goes into the disposer - usually attaching the drain line to the underside of the countertop.

Could that be the problem - that you didn't have the high loop?

Jdoll42 · Feb 26, 2008

SteveW said:
As a non-pro, I think that if you don't use an air gap, you are required to do a "high loop" of the DW drain line before it goes into the disposer - usually attaching the drain line to the underside of the countertop.

Could that be the problem - that you didn't have the high loop?

Possibly, maybe, maybe not. The dishwasher by default takes the discharge line all the way up the back of the dishwasher then back to the floor again before going through the cabinet to the sink drain. I don't know if that would count as a high loop or not. Hmm....

hj · Feb 26, 2008

disposer

The centrifugal force of the disposer occurs at the grind plate, not at the top of the disposer. If it were a problem pushing water into the dishwasher, it would also push it out of the air gap and onto the counter top.

Gary Swart · Feb 26, 2008

The high loop goes over the top of the washer and is normally attached to the underside of the counter top. It does not sound like you had done that. Some local enforcements require an air gap which is an device that is on top of the counter and has an intake hose and an outlet hose. Other areas just require the high loop. The air gap is legal in any jurisdiction and is the safer way to go.

BAPlumber · Feb 26, 2008

jdoll42 said:
Yeah, they don't require an air gap in the dishwasher discharge line, but you sure as heck can't run it into your garbage disposer. Seems odd to me...

never really thought about it but it makes sense. the disposal could possibly push waste into the dishwasher hose (regardless of airgap). Might be a local amendment.

hj · Feb 27, 2008

disposer

The disposer grind plate is a pump. It sucks out of the disposer and pushes into the drain line. It cannot pump out into the dishwasher. The only reason for the high loop is so when the sink is plugged the water cannot fill it and then drain down the line into the dishwasher.

Jdoll42 · Feb 27, 2008

hj said:
The disposer grind plate is a pump. It sucks out of the disposer and pushes into the drain line. It cannot pump out into the dishwasher. The only reason for the high loop is so when the sink is plugged the water cannot fill it and then drain down the line into the dishwasher.

That is kind of what I thought. So then my question is what is the difference hooking my dishwasher discharge up to my disposer vs. hooking it up to the other sink? If the other sink gets plugged water will still try to go back up the dishwasher discharge hose. (Isn't there a check valve in the dishwasher to prevent this anyway?) I'm beginning to think this inspector was just having a bad day and wanted to pass it along to me too....

SteveW · Feb 27, 2008

This makes no sense to me. Disposers have a fitting on them expressly for the purpose of attaching a dishwasher drain hose - that's the standard thing to do (again, providing that code is followed re: high loop or air gap).

whats up · Feb 27, 2008

if your plumbing inspector is goeing by the book,code states that no dishwashing machine shall be directly connected to a drainage system or food and waste disposer without the use of a approved dishwaher airgap fitting on the dishcharge side of the dishwashing machine.

Garbage Disposer Code Question

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