Finally... the exciting day has come! Slowly I started to add some water to the filter chambers, to test the home-made bulk heads.
Not entirely unexpected, one failed completely. When I drilled the hole with a 7/8" wood spade drill, I should have placed some wood on the back of it, or drilled from the other side. As the drill broke through, it broke out a piece of wood along with it. I hoped that the epoxy would smooth it out, but the rubber gasket wasn't flexible enough.
So, after removing all the water, and drying it off well, I epoxied the bulkhead into the hole. We shall see if the 5 minute epoxy bonds and holds well. For now, things are dry.
Without further incidents, I filled up the tank. Had a little issue priming the powerhead, which sits on the bottom of the back chamber connected to the spraybar. I just need to disconnect it to purge all the air. This might be an issue if the GFCI for this tank trips, but the CO2 still bubbles and fills the pump up with gas.
Since I mentioned GFCI... really good little life insurance to have for a few bucks. With one hand in the water, trying to wiggle the pump, and the other plugging and unplugging the power chord, I managed to trip the GFCI once. Without it... who knows.
Filled up the tank to the top. There was no sagging, and just a tiny little bowing of the brace-less top rim (4mm).
After a night without incidents, I siphoned all the water from the top tank to the bottom. And ran into another, again not entirely unexpected, issue. The "dry chamber" in front had a little leak on the bottom. It couldn't be from the main tank, which was epoxied all the way around. Sure enough, I missed a little spot on the bottom of the second chamber. I quickly removed the water from there and now I am pondering if I should silicone it or use some more of the 5 minute epoxy to repair the spot.