I have a new acrylic shower pan to install that came with a drain
fitting that screws on from underneath the pan. That part of it I
understand. There is a rubber sleeve that is about 1/8 inch thick and
about 3 inches tall that looks just like the one that came out of the
old shower pan. I can not figure out how that works.
The rubber sleeve moves around freely in the drain fitting, but will
snuggly fit around the PVC drain pipe. How can this sleeve seal the
fitting to the drain pipe if it moves aroung in the fitting? I notice
I can force it to fit tightly in the opening of the bottom of the
fitting. The fitting has a lip or flange at the bottom that is narrow
enough to squeeze on this rubber sleeve. Do I place it there and force
the whole shower pan on top of the drain pipe like that?
Struggling with the whole role of this rubber sleeve.

Thanks,
Brian