Jeff, your right, a bulkhead goes through the tank wall....you can also use an 'electical' pvc 'male' and female' coupling to do the same. Electric threads are straight...plunbing threads are tapered.
The couplings have a very small lip to work with, so the hole has to be perfect, so that the coupling has a place to contact and make a seal on the tank.
A real bulkhead is easier to work with, especially if your not using a hole saw to make the hole.

http://www.aquaticeco.com/subcategories ... gs-Economy


If your growbeds are 40 gallons...a 1 inch stand pipe may be a little big.
If you use a 1 inch bulkhead in the bottom of the bed....you could add a 1 x 3/4 or a 1 x 1/2 'bushing' to the bottom of the stand pipe and experminte with your fill and drain times.
A 'reducing coupling' is what goes on top of the stand pipe, if your doing the 'Affnan' style bell siphon.