LukeOscar,
I also had a similar idea about the 5 gal bucket as a canister filter and I learned some interesting things during my build. I'm attaching pictures of what I came up and some additional recommendations.
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So, I ran into a few problems. 1) the stock lid from lowes was not watertight as you might have figured out from the compression collar that I had to build to keep a good seal with the pump running. Once that was assembled, it worked out great. 2) another problem with lid is that it does not resist cyclic fatigue stress very because after about 4 months of operation and a normal weekly cleaning schedule with turning the pump on and off for maintenance caused the lid to crack near the PVC/lid junction. The lid also expanded outward when the pump was on like you said but in my case, that weekly fatigue stress caused failure one day after the four months when I secured the pump. Water just started pouring out of the crack as the filter depressurized. The crack might have also come from residual stress that was caused during assembly because the holes I cut for the 1" PVC you see in the pictures were designed to be interference fit to maximize the watertight integrity with minimal silicone at the joint. Based on the crack, I am planning on getting a hold of a plastic injection molding machine to cast a new lid that will be thicker which should help with the prevention of the fatigue failure. The filter was plumbed in to my sump and served as an internal recirculation filter so water was pulled from the sump, sent through the canister filter, and then pumped through a UV sterilizer and back into the sump. The pump was rated for 300GPH at 1ft head. The thing to think about is the long term use of the bucket as a filter. With the right lid and connections, it should work out great; just do some more testing maybe. I hope this helps, post any questions you have them.
