Periodically I get water under my kitchen sink and I can't figure out
why. (Actually, I can figure out where *some* of it has been coming
from: The valve for the hot water supply line had a small link. That
has been replaced and I'm confident that is no longer a source.
However.....)

After fixing that valve I *sometimes* get some water. A few other
details:

1. Plumbing: I have three traps under the sink. One is on the
disposer. The 2nd is for the non-disposer side of the sink. The third
is for the dishwasher drain.

2. Dishwasher Plumbing: My dishwasher is plumbed in the
loop-dishwasher-drain-high-under-sink and put it into a vertical PVC
pipe into it's own trap. This trap is downstream of the two sink
traps. (The sink traps go into a 'y', and dishwasher trap then enters
through another 'y'.)

Yesterday I watched VERY carefully while the dishwasher was going
through a cycle to see if anything was coming out of that drain.
Nothing. Totally dry.

My next theory is that, if the situation is right, using the disposer
causes some sort of pressure in the line that causes trap watter to be
pushed up through the vertical dishwasher PVC. (By the way, after
the second 'y' the pipe is horizontal for probably 2-4 feet before it
drops to the basement.) So if there is debris in that horizontal
section, could the path of least resistance be up the dishwasher drain,
rather than down the drain?

Is it better to drain the dishwasher into the disposer like I've seen
discussed?

Thanks.

Jim