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.