Originally Posted by MikeYQM
A Lifereef HOB
overflow is the way to go if you can't drill. No need for backup pumps etc to keep a siphon. They do not lose siphon.
Drill an anti siphon hole(s) in the return line just below water level and keep enough space in the sump for water to drain back into if the power goes out. Set it up, test, test, test.
I use a pair of HOB
overflows on my 75, each of which has a backup drain. I have a traditional HOB
overflow on my 37. The anti siphon hole trick works pretty well, but mine are all just above the water surface. (I drilled the ones on my spraybar so they directed the water back down into the tank.) I did almost overflow my sump doing a water change last weekend becasue my anti-siphon holes apparently had become somewhat clogged with algae. I got lucky and the water filled right to the top of the sump, but no further.
You can also get a one-way PVC
check valve to prevent back-siphoning through your returns. I don't think they are all that much, especially when compared to a remodel necessitated by a flood.