Those are amazing 3d backgrounds. I have always loved these. Saw a video once on a DIY for 3d background step by step with all the supplies you would need. Really caught my attention and would love to try my hand at it one day.
I decided to add a few 90 degree elbows to get the plumbing to sit more flush against the back wall of the tank. Drilling a perfectly measured hole in a 3D BG is harder than you think. The surface is uneven, where to measure from? I basically just eye balled it where I wanted the returns, said "screw it" and popped in two holes. It's easier to line up the plumbing with holes already in the BG, than it is to match up the BG to plumbing. I hope that makes sense.
Also do yourself a favor mark which side is which on the plumbing so they line up to the imperfect hole you just drilled. Oh and paint the back. Do it right from the get go.
^ even though the above has water in the tank, it is a complete FAIL.. I tried to use the trim on the tank to hold down the BG but it floats so strongly that it was pulling the 3 pieces away from one another. You can see it if you look closely. This is where the Great Stuff "pond foam" came into play.