K so here is the plumbing as it currently sits (the pipe isn't welded into the bulkheads):
Check out this clearance:
Entering the sump:
Right drain is the main, it goes lowest into the sump so that the end is submerged in water. This drain runs a full siphon and is controlled with the gate valve to be silent. Middle is the stability or backup which handles mild fluctuations in flow; these two together are a herbie style drain. The left one is an emergency one which will be set up with no air vent so that it runs full siphon and then flushes if the water level in the rear box ever gets beyond a certain point because something has happened to the main, and stability/back up drain. The stability drain will end about an inch above the water so it makes just a little bit of noise to aid in tuning the main drain, and the emergency is set up so the water falls a good 6 inches so as to alert whoever is around (hopefully me) that there is a problem with the main and backup drain.
That last photo is more or less the view you'll have (minus the return plumbing which isn't really started yet) when you walk past the tank into the room. Pretty clean.
Two things I need advice on:
First, how do I secure the plumbing into the bulkheads? I've used teflon tape and just jammed it in with good success in the past but I'm sure somebody has better advice for me. Is there a specific type of solvent you can get that will weld ABS to PVC, or do the dissimilar plastics not like to bond?
Second, does anybody have suggestions on how to secure the plumbing so the bulkheads aren't supporting the weight of the plumbing? I'm sure there's a good way to do it that won't hinder removing the plumbing in the future if needed? Some sort of hangers or something?
Edit: Just for clarity sake, I plan on putting the unions on the vertical run of the drains, right above the plastic trim of the tank, so basically they'll all sit just lower than that gate valve on the main. If anybody thinks I need more unions I can add regular white ones after the pipe runs under the tank so that it looks pretty outside. I'll be able to get away with install and maintenance with just the single union on each though I'm pretty sure.