How does the Wedi drain attach to the actual drain pipe? Should the drainpipe be in place so that the drain connects when the pan is lowered into place?

Wedi drains are compression fit drains, I found some details instructions on the Wedi site and will add to the listing. I have also added a Wedi installation video that shows you how to install the drain to the shower base, then in the middle of the video they show you how to connect the drain assembly to the shower drain. (these directions are for standard 2 inch drain pipes.)