Design Flaw: Air Gap on top of Kitchen Sink

[LilyT]

When dishwasher is not getting used frequently, the food debris in the garbage disposal can built up to clog the last section of the dishwasher drain pipe, as illustrated in this diagram.

When you use the dishwasher, not aware of this blockage and leave the kitchen or your house, misfortune will happen. Dishwasher's waste water shoots out from the air gap opening, which
1) may not face the sink (air gap cover can freely turn 360° and you might have accidentally bumped it), or
2) the opening is just a plain design, not like a kettle spout which accurately directs water with minimal dripping. As dishwasher drains, the waste water keeps gushing out from this opening, water flows everywhere, no matter your sink is undermount or top-mount. The top-mount sinks usually come with convex/rounded rim, I never saw a model with a high dam around it to keep the water in.
Now water overflows to your kitchen counter, to your hardwood floor, and you are not around to catch this unfortunate incident in time. You end up with a bigger problem.

The alternative to air gap is high loop, that is, to clip the pipe under the cabinet ceiling. As dishwasher's motor pumps hard to drain, the pressure should be strong enough to flush/unclog this type of blockage near the pipe end.

Theoretically, the top of the high loop needs to be higher than your kitchen sink/counter, so that, in case the sink is fully backed up to the rim, the dirty water won't backflow to your dishwater. But how frequently can this happen?

When I compare the chance of blocked pipe end due to infrequent dishwasher usage versus a fully backed up kitchen sink, I found I came across always the former scenario, it happened multiple times to me and my tenants. Yes, it caused water damage to my hardwood floor!

Ideally, I wish the manufactures can redesign the air gap opening to be a spout. So far I haven't found such a model in the market yet.

If you have a better solution, would you please share?

Thank you in advance for reading!

 

[Geofd]

I have always used the high loop

 

[Jeff Handy]

Agreed, unless it is required and you will be inspected.
After inspection, you can remove it and splice the drain line, and hang up a high loop.
Put a nice hole filler plug in the empty hole.
The code often requires it, but who is going to pay for your flooding damage?
Maybe there are some air gaps that work perfectly?
Anyone on here have experience with fool proof ones?
Sorry if I am throwing gas on a fire.

 

[Jeff Handy]

I think another problem with the high loop is that if you attach the dishwasher drain hose to a tailpiece with a tee for the drain, and the drain line gets partially clogged, the disposal can try to force gunk back into the dishwasher drain hose.

 

[frodo]

both of these will block at the same point for the same reason
the air gap fitting is not a check valve.

i have had inspectors turn a blind eye at the high loop and have had them tell me that after final inspection do what you want
i do not install air gap fittings, but make no mistake, they are code,

 

[havasu]

You know, just thinking out loud, I have seen the knockout plugs only partially break away, leaving sharp edges on the inside of the disposal inlet. Pull the hose from the disposal and put your finger to feel for any rough spots, and if so, clean up the edge with a dremel. I also do a simple rinse so no food goes into the dishwasher in the first place.

 

[LilyT]

I think another problem with the high loop is that if you attach the dishwasher drain hose to a tailpiece with a tee for the drain, and the drain line gets partially clogged, the disposal can try to force gunk back into the dishwasher drain hose.

Hi Jeff, is it possible for you to sketch a picture of what you described in your 2nd reply? I want to fully understand the pros and cons before I change my air gap to the high loop. Thanks for your reply!

 

[LilyT]

both of these will block at the same point for the same reason
the air gap fitting is not a check valve.

i have had inspectors turn a blind eye at the high loop and have had them tell me that after final inspection do what you want
i do not install air gap fittings, but make no mistake, they are code,
View attachment 25771View attachment 25772

Yes, the high loop will have the same blockage, but I hope the dishwasher’s motor will be powerful enough to flush the gunk out. If not, it will be reflected as an error code on the dishwater’s control panel, and too bad, fixing it will involve much more work compared to the air gap leakage.

 

[FishScreener]

UHHM!!! The air gap is there to prevent the garbage grinder pushing ground waste and water back into the dishwasher, if there is a restriction in the waste line.

 

[frodo]

UHHM!!! The air gap is there to prevent the garbage grinder pushing ground waste and water back into the dishwasher, if there is a restriction in the waste line.

NO sir , I beg to differ
The air gap is there to prevent the dishwasher from syphoning the dirty water back into the dishwasher
by means of an air gap.

 

[FishScreener]

NO sir , I beg to differ
The air gap is there to prevent the dishwasher from syphoning the dirty water back into the dishwasher
by means of an air gap.

Try this with high loop. Disconnect and cap the drain line. Fill the sink with water with just a bit of food coloring added, and run the garbage grinder. Open the dishwasher and look in the pan. It will now be full of colored water.

Try the same experiment on one with the air break installed, and it will pump water out of the air break, and it doesn’t get to the dishwasher.

I’ve had to clean up several of those messes. Lesson learned.

And, if the garbage grinder is used per the instructions, and the dishwasher used on a regular basis, you will probably never see the problem. The flow from the dishwasher will keep the line to the grinder clean, and if you add waste to the grinder while the water is running, and the grinder is on, it will flush it down the drain. The problem with the grinder putting solids back into the line from the dishwasher occurs when you over fill the grinder with it off, and then back up a bit of water before you turn it on.

Also, I install a tailpiece with the connection for the dishwasher drain, instead of hooking to the grinder. Simplifies thing in my mind.

 

[Riickk]

Odd thing is, it used to be building code that finish floors in kitchens be made of waterproof material.
Then, somewhere in the ? 1990's ? wood flooring in the kitchen became fashionable.

At least with linoleum, vinyl, or tile, a kitchen flood didn't necessarily mean expensive repairs.
....Shrug...

 

[LilyT]

Odd thing is, it used to be building code that finish floors in kitchens be made of waterproof material.

I have tile floor in the kitchen on the front side of the sink but hardwood floor on the back side of the sink. The countertop on that side is used as a bar area.

 

[Helper Dave]

These are all reasons we prefer to build stand-pipes in new construction and remodels where we can. Sure, any pipe can clog and back up, but 2" PVC will keep clear for a long long while.

It can be real tough to retro-fit a 2" stand-pipe into older homes, though, so you gotta meet code the best you can.

 

[LilyT]

Try this with high loop. Disconnect and cap the drain line. Fill the sink with water with just a bit of food coloring added, and run the garbage grinder. Open the dishwasher and look in the pan. It will now be full of colored water.

I’ve had to clean up several of those messes. Lesson learned.

Also, I install a tailpiece with the connection for the dishwasher drain, instead of hooking to the grinder. Simplifies thing in my mind.

Thanks for replying!

In the cases you had to cleanup the messes, how high were the drain hoses hanging?

I wish garbage disposal’s sucking power is drawing water downwards to its exit hole not sideways to its dishwasher hole. Under this assumption, in your color experiment, the water shouldn’t go to dishwasher. Unless you’re also running the dishwasher at the same time and creating some kind of pressure difference for the water to climb over the top of the high loop.
In your last paragraph, you mentioned you’re not hooking the hose directly to the grinder but thru a tailpiece. How does this help alleviate the situation?

 

[FishScreener]

Thanks for replying!

In the cases you had to cleanup the messes, how high were the drain hoses hanging?

I wish garbage disposal’s sucking power is drawing water downwards to its exit hole not sideways to its dishwasher hole. Under this assumption, in your color experiment, the water shouldn’t go to dishwasher. Unless you’re also running the dishwasher at the same time and creating some kind of pressure difference for the water to climb over the top of the high loop.
In your last paragraph, you mentioned you’re not hooking the hose directly to the grinder but thru a tailpiece. How does this help alleviate the situation?

The ones I’ve had to clean up after the loop let things flow back into the dishwasher: one had the loop hooked to the bottom of the counter with an Adel clamp, which is aloop clamp used in aircraft which has a rubber strip on it to isolate vibration. In aircraft they are used to secure hydraulic lines. The other they had wired to two sink clamps.

The one with the Adel clamp had filled the dishwasher pan with waste which looked like vegetable grindings. The other, the old Jewish lady across from a house I rented in Las Vegas when I was going to school, was peeling a whole bag of potatoes to make something for one of the Holidays, and did them in a sink of very warm water. She then pulled out the stopper plug, and tried to run the whole mess down with hot water. which of course made potato paste in the waste line. She didn’t figure out that she had a problem until the pan on her dishwasher had filled up and started running onto the floor. At which point she ran screaming out the front door. I went to help her and ended up spending a day to snake the waste line, and help clean up the mess. Her lawyer sons showed up when I was almost done, and paid me $250 for the day, which when you’re in the starving student mode, is really helpful.

All garbage grinders act as pumps, and if you follow the instruction and turn on the cold water before you start the grinder, and then add the waste in slow steam instead of a big glob, they won’t ever run the waste back up the drain line from the dishwasher.

But, folks rarely read and follow directions, as evidenced by the post that started the thread, so I have started to use the tailpieces with the dish’s washer tie-in, which eliminates the problem. But still, if you use a loop without the air break, above the sink deck, and have a clog, you still run the risk of getting things flowing back to the dishwasher.

 

[Mitchell-DIY-Guy]

If you are getting THAT MUCH CRAP in your dishwasher drain line--the problem isn't the line, the air gap, or anything similar. It's your knowledge of the specifics of your dishwasher and how to use it.

Many American design dishwashers had some kind of crude disposal system; I know my old GE did. A much better design was the Bosch that replaced it, with an extremely fine stainless steel mesh filter. Nothing that could possibly clog a drain line would get through that fine filter. All you had to do periodically is take it out and clean it. See the photo? See that super fine mesh? That will hold back ANYTHING with the potential to clog a drain line.

I've run a number of dishwashers over 40 years and NEVER ONCE had a clog in the line. But then again, I rinse the food off the plate and that goes down the disposal in the sink. I don't knowingly put solids into the dishwasher.

I have a brand new home in NC and no air gap on the dishwasher.

 

[Jeff Handy]

Peelings and trimmings should be caught by the basket strainer, and scooped up and dumped into the garbage.
Dirty plates should be scraped into the garbage, and the remaining bits rinsed into the disposer.
Grease should be drained into an old food can or other disposable container, not down into the disposer.
People who treat the disposer like a magical garbage can will suffer for their lazy foolishness.

 

[LilyT]

If you are getting THAT MUCH CRAP in your dishwasher drain line--the problem isn't the line, the air gap, or anything similar. It's your knowledge of the specifics of your dishwasher and how to use it.

Thanks for your reply!
In my cases, the blockages are not caused by the food crumbs coming from the dishwasher where the Bosch mesh can catch, but from the garbage disposal. If I haven't used my dishwasher for a while (e.g., a month) and I start to run it empty loaded, waste water will come out from the air gap and I have to insert a pipe cleaner brush to unclog it. Being fully aware of this hazard, I remove most of my food scraps from the kitchen sink in my daily food preparation, I only have the need to use garbage disposal occasionally under running water of course. Still I found the end section of the dishwasher drain hose is too easy to get clogged. A 1"~2" clog is enough to send the water out of the air gap opening.

 

[LilyT]

so I have started to use the tailpieces with the dish’s washer tie-in, which eliminates the problem.

I'm not familiar with plumbing pieces. I'm trying very hard to imagine what you mean here . If possible, will you please draw a sketch of your connection?