Hey oughtsix-very curious as to how you set up the cornelius keg to make it work as a canister for your filter. I've looked at diagrams and I don't know what to keep and what to toss and what to replace the inlet and outlets with. Looks like the perfect container.
I just unbolted the pin lock connectors from inside the keg and found some stainless steel bulk heads that I used with barb fittings to connect the hoses (I am pretty sure I ordered them from Grainger and I had to enlarge the holes in the keg a bit... with a Unibit step drill). The supply line went to the top of the keg and the return to tank line drew from the bottom of the keg. I did not know about Uniseals at the time... I suspect they would work quite well in the 3/4" to 1" size and hold the pressure without an issue. I suspect a well build polypropylene bulkhead with thick rubber washers would work too... I know PVC bulkheads won't seal well and it will probably leak. The pump has to be before the keg to push the water through and keep the keg at a positive pressure. I used a fair sized little giant pressure rated pump.
I used a short fat Cornelius keg instead of a taller thinner one because the shorter one fit in the stand under my tank. The shorter fatter ones also have a bigger opening on the top which makes them easier to put the media in and remove it for washing. I used many layers of thick coarse porret foam for my media which worked as mechanical + biological media. With the keg, bulkheads, misc plumbing, pump and foam I was into it for well over a couple hundred bucks by the time I had it working well.
After experimenting with the Corney keg for about a year I decided that a huge capacity canister was not all that I had expected it too be. It really didn't add anything to the tank and was a REAL hassle to clean, so it didn't get cleaned very often which caused high nitrate levels in my tank. Everyone on the web (this board in particular if I recall correctly) told me not to do it and it would not be worth the effort. BUT there are some things that I just have to try for myself!... I did, and they were right!
