Fluid bed construction video
This is the fluid bed I assembled. I had planned to use the usual male and female PVC pipe fittings, but while I was at Home Depot I noticed the PVC pipe union. The advantage is that it holds the filter medium much more uniformly and tight. Also you can use thicker filters and it won't destroy filters by threading on them.
The downside is that a PVC union costs about $8 vs. $4 for a combo of male and female fittings. You also have to cut your filters into 3" circles but that takes less than a minute.
This one is made for 2" PVC pipe but you can easily find them in 1-1/2" and 3" too.
"I care not for a man's religion unless his dog and cat are the better for it." -- Abraham Lincoln