It looks like having the pump suck the water back into the pond be my
best option. Would I be able to thread a pipe through the drain plug, so
that I could put an elbow on the inside and a reducer on the outside?[/quote]

What type of filter are you building here? As for the PVC- you can use Uniseals to connect your pipes to the tank. Here is a link- but might want a different supplier as I believe there is a high cost to ship to Canada.


http://www.aquaticeco.com/index.cfm/.../8600/cid/2009