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?