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I ended up making a mistake and turning the brass hose fitting 90 degrees, I think the bellow configuration is probably better for our particular setup.
Assembly
I measured the depth of the fittings at 3/4". I doubled this and added 1/4" to get the small pieces for connecting the elbows and tees together. The saw eats up some amount of the material when you cut, so I like to measure-cut-measure-cut... to make sure the pieces are as long as I want them Try to get the cut nice and straight. If your cut isn't perfect, measure from the part that sticks out the most, that is the part that will bottom out when you put this together, all the imperfections at the pipe ends will be inside the fittings, only max length discrepancies will be visible. Remember to clean up the dust this makes and get all the mess off the ends of the pipe. It helps a lot to have the pipe secured when you cut it. You may want to try pressing these together, don't do it. The fittings are tapered and require a mallet to get in all the way, and are nearly impossible to get back out once together. (don't worry about when you cement them together, they go right in with the cement).
I then cut the long segments, 20 inches left 1 inch extra for the way I drilled 36 holes.
Next comes gluing. This must be done in a very well ventilated area, I'd suggest going outside. I didn't use primer, you may want to. Follow the instructions on the cement for actual technique. Remember to keep the positions of pieces correct when putting this together, and don't get them rotated wrong. I'd suggest putting the short pipes into the corner fittings, then the corners on the outer long pipes, then the tees on the inner long pipe, then then add the outside long pipe assemblies to the middle (this requires doing 2 joints at once, so be quick), and finally add the bushing reducer.
The brass fitting screws into the plastic threaded bushing. Pipe threads are tapered, they should get tighter as you screw them in. If the fitting doesn't get tight, it probably doesn't seal. Mine got harder to turn when the hex part you grab with the wrench ran into the plastic, do not mistake this for it getting tight.
You should use teflon tape to wrap the threads to make it fit tight, but I just used hot glue to seal around the fitting, this should work for a vacuum system.
Drilling the holes is the hard part.
