Here's my blog on uniseals:
Uniseals are available at reasonable cost (Way cheaper than bulkhead
fittings) from Aquatic-Eco-Systems. If you are going to be a pond hobbyist
you really need one of their catalogs. All their stuff can be ordered
online, but having one of their catalogs to look at is in itself
entertaining and educational. See their uniseals at
http://www.aquaticeco.com/index.cfm/fuseaction/product.detail/iid/8600/cid/2009 .
Incidentally, uniseals seal because of the interference fit. For example,
to connect a 4 inch PVC to a 55 gallon drum, (you WILL need a hole saw kit,
see Harbor Freight at
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=36222 for
the best deal on those) you obtain a U400 uniseal and cut a 5" hole in the
drum. Insert the uniseal (it will fit sloppy, but don't worry, that will
soon change). AES (AquaticEcoSystems) recommends using Windex as a
lubricant, but my experience is to get some SILICONE GREASE. Before
attempting to insert the pvc, you will need to chamfer the edge of the pipe.
You can do this with a rasp or file. Lubricate the pipe with the grease and
push into the uniseal (This WILL take some effort, but perservere and you
WILL be successful). Try not to push the pipe further in than you want,
beause pulling it out to where you want it can be problematic.