Uniseals are very easy to use. Simply use a hole saw to make the correct sized hole, insert the Uniseal. After the Uniseal is in place, you can slide a piece of pvc into it, sometimes you may have to apply light lubrication (or get it wet) to the pvc to get it slide in. Once the pipe is in place you now have a water tight fitting.

This is a 3/4 Uniseal. These require a a hole made by a 1.25 inch hole saw. These can be used in Recirc Mod Kits.