as a new pool owner (last year), I was a little confused by this initially too..

The Polaris is a clearner (and a darn good one!). It is pressure side (booster pump) and uses a bag to collect things.

A Vacuum is different. It goes on the end of a pole and is flexible plastic. You connect it with a hose into your skimmer (remove the basket). My PB gave me a plug (PVC section with cap on the end) for my second skimmer so all the suction would go to the other skimmer (and vacuume).

It works by channeling all the filter pump suction to the vacuume head. The flexible plastic allows it to maintain decent suction over a bigger area than the end of the hose.

Normally, the filter-pump basket and filter would catch whatever you suck up. Since you know you're sucking up crud, you'll clog your filter quickly. Vacuume to waste is a backwash value setting that allows you to bypass the filter and just dump, the water. You'll drain your pool a little, but you won't clog your filter.

I don't have a drain to waste position on my backwash valve. So it's all hypothetical to me

Robert