Hi, I have a draining problem with a Bosch SHV4803-UC12 dishwasher.
Under normal operation, the basin dosen't drain.

When I disconnect the drain hose from the wall and redirect it to a
bucket, it drains fine. The motor works, I can see water going through
the little transparent plastic trap thing under the panel, and I can
measure 120VAC getting to the motor. It *sounds* like it's working
fine too, but I can't be sure.

The household-end of the drain hose goes into a pipe in the wall, not
any visible above-sink air trap or anti-siphoning mechanism that I can
see. It just disappears into the wall, not the garbage disposal,
y-connection, etc.

When I pour water into the drain hose into the wall from above a
certain level, water continues to go down, and there is little
blockage. If I pour too fast, it'll back up, but it quickly clears.

If I take the drain hose and lower the end to a foot or so above the
floor, water comes up, indicating there is water sitting at that level
somewhere else, and I can't pour water down.

This indicates there is water above the drain somehow, and when I blow
through it I'm somehow blowing this extra water through the pipes. I'm
really not sure what's going on. If I stop blowing before it's clear,
I can hear water sloshing in the pipe back and forth, as though
something is pushing it back.

In all cases I can blow through the hose, and after *much* difficulty,
can eventually clear the hose and blow air, though it's still
difficult. When I then pour water in, it again backs up. We've tried
drano, etc., to clear it, but I'm pretty convinced it's not a gunk
blockage, since it'll take a LOT of water if I pour it in from above a
certain level.

A plumber told us that this is normal and nothing is wrong with the
drain in the house, and that sometimes a dishwasher needs backpressure
to keep the pump primed. But I've been reading that often this is to
prevent unwanted siphoning of the drain.

But I know the drain in the dishwasher can pump water into a bucket.

Is the dishwasher drain motor supposed to overpower the backpressure in
the drain? In other words, is my motor somehow weak and damaged,
enough to pump the water into a non-backpressure bucket, but not enough
for the drain? I don't get it.

Is my drain clogged, or do I need a new motor?

thanks
michael