[untamed]

Originally Posted by jslaney

So I will be installing my plumbing tonight and I want to cofirm that the only way to prevent your return line from vacuming half the water out of your tank should your pump fail is to drill a hole at the highest point on your return line. How big should that hole be. I am assuming I want to drill it in a direction such that water does not squirt out the top.

Clear as mud?

Thanks,

Jon.

The hole is certainly NOT the "only way". If your returns run over the top of the tank, you can stop siphon by not extending those returns deeply in the tank. My returns only break the surface by about 1 inch, so 1 inch is the maximum siphon.

Of course, there is always using a check valve.

Finally, a siphon break hole doesn't have to be at "the highest point"...it just becomes the point where the water will siphon down to... before it sucks air and breaks the siphon. In the case of my 'fuge, that hole is actually 3/4" below the water line. When I kill the pump, it back siphons 3/4" of water before this hole becomes active.

When the pump is on, water squirts though the hole but underwater so that causes no problem. However, since the hole is underwater it is easily clogged by algae and critters, so I would not recommend this for a main tank.

So...a hole just above the waterline might be the most reliable placement for a siphon break hole.