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Dishwasher Check Valve / Backflow Prevention (External to DW)

I have a major renovation finishing & installing new flooring in the Kitchen is part of it. Well, one of the things that the Plumber missed was to shakeout any clogs due to the @#$! tile & drywallers insatiable need to put their debris into drains.

The result of this was a clog which caused the kitchen sink & dishwasher to back up. When the water got above the air gap (properly looped @ >18"), the sewage/.grey water overflowed into the dishwasher. Once this occurred, my new flooring installation had to be pulled up, dried out & will be re-installed.

Everyone, incl. my Plumber insists that the air gap/ inverted 'U', properly done is all that is required. I feel that a check valve ON the Drain Line is really the proper installation to prevent this kind of back up & consequently, damage/un-healthy discharges if/when there is a backup. It is my opinion that it is better to have backflow go into the sink (which is deep), than into the dishwasher (which does not have much depth/capacity).

My question is this:
Lack of Code Req'ts be danged, I'd like to know if there is a downside to installing a check valve that is external to the dishwasher?

Thanks for any ideas.

Timothy Miller
Re: Dishwasher Check Valve / Backflow Prevention (External to DW)

What no vent pipe on this waste line for the sink and dishwasher? Renovating was the perfect time to add one so the sink & dishwasher waste is plumbed so air from outside the home allows for the water to run down the pipe.

The back flow valve would be installed on the main waste pipe stack to control back ups into the dishwasher& sink...

Re: Dishwasher Check Valve / Backflow Prevention (External to DW)

Anyone have any thoughts on adding the Check Valve?

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