I posted this in plumbing as well, hope that is OK. Until I am clear about how "loop" is, I am wondering if it is safe to use the diswasher itself. Here is the post and brief followup:

New dishwasher installed last year without airgap. Think/hope contractor used the "loop" system discussed elsewhere on this forum.

Suddenly, WITHOUT dishwasher running, water from sink went to bottom of dishwasher, did not drain, but ran out bottom of dishwasher onto floor. Sears came out (does anyone else now believe that Sears is beyond terrible?) Technician said nothing wrong, guaranteed that an undercounter airgap will resolve issue. I read here never to do that. So.... Any ideas appreciated. Thank you.

"high loops" are often configured improperly. My new DW with "professional" install was botched this way. Knowing what to look for, I fixed it myself. Very easy. The peak of the loop must be secured above the level of the sink-lip....right up there under the counter. However, even then, if your sink is really full the surge from opening the drain can push water over the high loop. Once that occurs, the siphoning can continue until the sink's empty. I suspect that's what happened. An air-gap installation will prevent this. That's why many people have suggested that ALL codes, not just some, should require air-gap installs.

Your dishwasher will not drain unless the drain pump is operating. Once the siphoning action began, you were doomed unless you recognized it and stopped the drain immediately.

"The peak of the loop must be secured above the level of the sink-lip....right up there under the counter."

Securing it to the bottom of the counter (and making sure it stays there) is all that is required.

While it could still cause a backup if the sink is filled to overflowing, kitchen sinks are not normally filled that high.

The important thing is to get the loop high enough that normal use of the sink never allows water higher than the loop.