Also commenting on the overflow design: <The pic is rather small so I might not get all the details right.>
It is true that when the power is out, the water in the display will only drop down to the level of the over flow & stop. However, you would have lost the siphon in the overflow. When the power comes back on, the return pump will pump, but no water can get back to the sump & you will have a flood. This is a fatal flaw!
To do the PVC
overflow safely, you need to have a way of preventing the loss of siphon. You normally need 2 U-joints - one inside & one outside the tank to preserve the siphon. I think the video has it, but I can't see the outside loop clearly enough to see if it is failsafe.
You can also use an alternate design where the intake is at the bottom of the tank & you control the water level with a loop outside the tank. This is a bit safer for preserving siphon but has a draw back as well.
Personally I would use 2 siphons, each capable of of carrying the entire pump flow. <A 1" ID pipe will do 750 gph
safely.> I would set the 2nd siphon slightly higher (say 3/4") than the first (but still beneath the tank rim). That way, when the 1st siphon entrain air (and you will, esp. with skimming from the top), the rising tank water can be drained by the 2nd backup siphon. You can then quickly see by the water level that you need to reprime the 1st siphon. <With white PVC
, you cannot see any air in the siphon loop & cannot prevent accidental siphon breaks before floods!>
Maybe I am too obsessive about floods ... but working with 100 gal
of water makes me very cautious ..... belts & suspenders all the way!