For in-tank plumbing use black pvc. You can buy it at Savko. It is much prettier than white and makes for a very professional look and is reasonably priced.
Painting the back of a glass tank looks far better then just placing something black behind the back glass even if you use the same paint. The air gap between the backdrop causes refraction reflection which makes the back a mirror at certain viewing angles. The mirror effect highlights anything growing on it besides not being the color you intended. Painting the back makes the back a solid color that looks great and consistent from any angle.
Not much is worse than a reef slide. It can scratch your acrylic or glass and kill your corals. All that live rock likes to shift around. Especially with all that water motion. I used a long 1/4" drill bit (doesn't have to be masonry) and made holes in my live rock and connected the pieces together using 1/4" clear acrylic rod. Much like a tinker toy set only the rods inserted farther so as not to be visible. Not only did I make my tank impervious to reef slides since all the pieces are interconnected, I can also create shelves, coves, towers, and caves, that gravity will not allow by just stacking the rock. Aquascaping options galore!
Don't glue any PVC fittings that you don't have to. Pressurized lines like plumbing off of a return pump should be glued, some bulkhead connections like the the drainline from the overflow. But why glue in your stand pipe or fittings off of an in-sump skimmer, or even the separate pieces of a durso? The fittings keep pipes and plumbing snug enough while allowing you to make quick effortless changes to your plumbing.
Eliminate or lessen the height of any waterfall in your system. Waterfalls create three undesirable things: Microbubbles, Noise, and Salt spray. Microbubbles are often undesireable to look at and scatter light. Noise imposes your aquarium on the rest of the room atmosphere. An aquarium should be seen not heard. Salt spray is ugly, causes salinity creep, decreases the life of electronics nearby, and degrades the surface materials of your hood, stand and any other surrounding materials.
My rule of thumb is less than 1 inch. My sump has no water falls. The fall over my display overflow weir is 0.5 inches. It's also whisper quiet.