Good morning Michael,

In answer to your first question, yes, a drain pan can be drained through the bottom if designed to do that by the manufacturer but, like you, I've never seen the application.

Regarding the second question about trapping the condensate line if there is no diagram on the evaporator cabinet illustrating the trap layout you'll need to refer to the manufacturer's installation instructions.

One of the great things about the internet is that many manufacturers now put their installation manuals on the net. I've used it many times to determine what was supposed to be done.

Good luck,

Don Norman