I'm rethinking the PVC/ABS plastic 'T' design a bit, and as of now... I'm torn between a high dollar stainless steel container, and a pre-manufactured housing like you would find in home or swimming pool systems.
I've found a few sources for the filter housing, and the price for one with dimensions in the range needed for a decent sized HHO Generator is around $40 - Going this route would provide me with a visible waterproof canister with a drain at the bottom, and a screw on, sealed lid with pipe fitting built in. I'm still researching that solution, as I have concerns about temperature.
Another more bullet-proof solution would be a Stainless container... but things start getting difficult if you don't have a way to work with the stuff. Cutting plastic/PVC/ABS is one thing. Cutting Stainless Steel is a hassle if you don't have the proper equipment and tools!
I'll be back with more...