I am going to be honest, the tank looks great, but your return has me a little nervous. I do see that you have a decent check valve to stop any flow back, but those can get clogged which could leave them in an open position. There seems to be a lot of water that could flow back into the sump at that point...more then the sump can probably handle. Your set up works well if you are home, but if the power goes out at night, there could be a mess. My suggestion would be to...
A: add a ball valve near where the bulkhead is so that you can turn off the return flow siphon back completely and then remove the check valve for cleaning.
B: Add some elbows to the return on the inside of the tank so that one is above the water line. Drill a hole (I just used a 1/4 bit) in the side of the top elbow (not the top of the elbow, or water will squirt straight up, you want the hole to point towards the water right at the water level), that way if the check valve fails, then the line will take in air killing the siphon. You can always turn the lockline towards the surface, but a fish could easily push down the lockline over time meaning more water in your sump aka, then on your floor. And with some of our luck, that will happen the day you are gone for a few hours :/