Heres another simple idea for the budget minded aquarist. You can make your own bulkheads with 1 male Thread/Slip PVC adapter, 1 female Thread/Slip PVC adapter, and a rubber washer.
While these may no be practical for use on thick glass tank bottoms, they are perfect for use on acrylic pre-filter (external) overflows and sumps. These simple, inexpensive bulkheads can also be used for any number of unrelated projects. I used one to mount a Squirrel Shield on a PVC bird feeder pole. The one thing you need to remember is, in aquarium and other plumbing related applications, the rubber washer goes on the outside (the dry side).