In ,
Pat typed:
But, why all the concern?

Because my washer does not seem to be operating properly -
it seems to need to have water added at times during the
various cleaning cycles as if water is leaving it for some
reason. I'm wondering if the water is draining through the drain
pump because there is no "up-loop" in the discharge line.

Likely. Also the sewer gases are coming up into your
dishwasher and entering your house 24/7. The dishwasher is
made to vent the air/moisture inside out into your house.

Here's a novel approach: RTFM! It even explains the siphoning action and why
it happens in 99% of the cases.