You can buy an Overflow Box for around $100 make your own overflow Box.or make your own overflow using PVC
I built my Sump with a PVC
overflow. I found a thread on how to make these on another reef forum. It seemed to work quite well for a few weeks until I lost my Syphon 2 times in the same day. Luckly, I happened to be sitting near the tank BOTH times and was able to shutdown the pump before too much water overflowed from the main tank.
Anyway, Air is getting into the system somewhere. I will be connecting the Airline tubing to a Tom's AquaLift Pump on Friday and will start testing again. My hope is that the pump will suck out any Air that might get into the syphon. Plus, if power is lost it will make sure it get's primed if needed.
I'm starting to think I should have just bought the CPR overflow Box.
I'll look for the thread and post it if I find it.
on your other question.. Not sure if you can seal PVC
with Silicone. But I think it would be much easier just to use PVC