I have 5 drain hoses from various appliances (dishwasher, laundry washer, AC condensate, water softener, water filter) that all have the standard regulated air gap to a sink.

I imagine drain pumps on these appliances could create enough pressure to blow their drain hoses completely clear of water, but in looking at a few examples, it seems that this is never done. In other words, it seems each of my 5 appliances leaves its hose full of water (from the appliance's pump) to the highest hose point.

That heightened water then creates a reverse pressure when the pump is turned off (i.e., when the appliance goes into standby mode). For example, my dishwasher needs to hold off 3-feet-elevated water after the drain with some sort of drain seal. A slight seal leak would retake the water over days and potentially stink up my dishwasher. Even if the seal holds perfectly, I worry that the water left in the dishwasher's drain hose could get stinky...I wonder if I'm misunderstanding this, so please correct me if I'm wrong...maybe there is no real problem (stink or otherwise) from leaving still water in these hoses for weeks.

Finally, my question: Is any appliance, especially a dishwasher, designed instead to leave its drain hose empty? Maybe a sump pump?

  • The pumps in these appliances pump water not air, so they will never blow their drain hoses clear of water at all.
    – brhans
    Sep 27, 2020 at 14:32
  • @brhans Ok. Seeing this actually led me to this question, so I did want to confirm that, thank you. If it were easy to blow out (or manually empty) the hoses for standby, would there be any harm in that? Generally, houses try to avoid standing water (especially for waste water with food/bacteria), so that's motivating me here, but it's mainly curiosity now. It's also odd that none of my appliances (except for my Beckett CB151UL condensate pump) spec the maximum drain hose height - I'm curious exactly how high the average dishwasher drain can pump water.
    – bobuhito
    Sep 27, 2020 at 14:50
  • The water at the end of a cleaning cycle shouldn't really be dirty though, it's just a rinse. And do you really go weeks between dishwasher runs? If so it'll get stinky due to dirty dishes sitting in it for weeks and the hose will be the least of your issues.
    – Kat
    Sep 27, 2020 at 17:47


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