I am finished with my PVC plumbing now! Hooray! After my adventure with the unions, the only thing left to do was get the draining water from the unions down into my sump.
Some background: my tank is 48 inches long, but my sump will be only 30 inches long. The drain and return holes are in the middle of the tank. Originally, my plan was to put my sump all the way to the left in the bottom of the stand, and have the drains pull the water over to the left, while it went more or less straight back up into the tank from the pump. I somewhat arbitrarily decided to do this because the less distance the water from the return has to travel, the fewer gallons per hour I will lose on the way up.
But it didn't work out that way. By the time I had the unions installed, I had dropped my drain plumbing down far enough that the only way to get it over to the left would be to move it all that distance horizontally with hard right angles on either end. This is not a very good way to do a gravity drain, because the water encounters a lot of not-flow-friendly situations that way. So I decided to put the sump all the way over to the right side of the bottom of the stand, instead. This let me drain the water more or less straight down into the sump. The return piping will have to do more curving around, but it will be flexible tubing and hopefully fairly amenable to doing so.
I thought about having two separate drains all the way down into the sump. There are people who claim this is the most effective way to drain a tank, if you have two drain holes. But the problem is they are close together, and draining right down into the sump made them get in each other's way like whoa. So I decided to combine them into one drain, then dump that into the sump.
Because PVC is a relatively inflexible material, this presented two challenges: 1) Making sure the two branches of drain were exactly as far apart as the drain holes, and 2) Making sure the two branches of drain where exactly the same length before combining into one.
I decided to focus on these one at a time. The immediate area where the two branches were combined consisted basically of two 45-degree elbows and a tee. When I put all the pieces I was planning to use together, I discovered that my branches were a little bit too far apart. I solved this by cutting down one of my 45-degree elbows so that it didn't span quite so far away from the tee I was using to combine them. Kind of hard to picture, huh? This is what that all looked like together:
You can see how the left piece is just a bit shorter than the right one. This got me to my target distance between branches. (If you're interested, the connecting pieces on each side here are 1" 45-degree elbow, small piece of 1" PVC pipe, 1 1/4" to 1" Reducing Bushing, and a 1 1/4" Tee. Right before I combined the pipes, I stepped them up a size to accomodate the extra water.)
Now I just needed to get them to be the same length. To do this, I just made the PVC connector pipe between the 45-degree elbows and the next piece, a slip-thread adapter, slightly longer on the side that needed more length. After I did that, I screwed on the bottom halves of my unions to both sides, and, hooray, they were the same length!
After I did that, I installed them under my tank to make double sure everything fit and was happy. It did, and it was!
The only thing that remained was to add a little bit more PVC to direct the water to where I want it to enter the sump. After I did this, I was all finished!
I have a tank there for measurement purposes, but it's not the one I will use for my sump. It's the same size as I plan to use (29 gallons) but this particular one has had some gerbil residents in the past and is no longer fit for fishies. It is very useful for planning plumbing, though!