CPR is a company that manufactures acrylic overflows.
Wai's used to carry them, and maybe still does, if you wanted to see one.

...and I'm guessing that a gravity fed larger drain line going to the sump is to compensate for a pump-driven smaller return line to the main tank.

HTH,
Mitch

Is this to ensure the siphon restarts in the case of a power outage (like the one I had this morning!)

Could you explain how this works?

in my experience, overflows made NO sense at all to me until I actually hooked it up and figured out how it worked by watching it. If you have a friend that's running a sump/overflow setup, get him to show you how it all works. That'll be MUCH easier to understand than reading about it.

when you're doing your return plumbing REMEMBER TO DRILL A SMALL HOLE just above the water level so if the power goes out, it doesn't syphon the water outta your tank thru your returns. I learned that one the hard way :(

I agree with that 100%.

-Richer

I have studied a few overflows in action, but I agree, I won't learn any better way than to try it myself. Just don't understand how I can run a powerhead (which is suppsed to never be run dry) to suck air out of an overflow?

Good advice about the siphon-stop, but I think I am going to sidestep that possibility by having my external eheim canister filter pull from the sump and return to the reef tank via a spray bar mounted above the water level.

still drill the holes, they're small and don't cause problems. they cause more problems if they're not there :)

I don't understand your concept behind the ehiem though..it can't pull nothin out if the power's off.

Because the holes in the eheim spray bar will be mounted above the water surface of the reef tank they would essentially serve the same purpose as drilling a hole in the elbow above a return line.

ie: the return line will not be below the water surface so it could not form a back-siphon.

Kind of confused me with the non-powered eheim comment?



Invigor and Richer, thanks a lot for this discussion, really helping a lot to bounce my ideas and plans off a couple experienced folks. Wish I could draw a diagram!

hey, not a problem. feel free to shoot away. I had many of the same questions you had before I got mine going. now due to space I don't have a sump :rolleyes:

If you can, the easiest way would be drill all the tanks with "in tank" overflows (you have small tanks so ripping them down to do so isn't that hard....just ripped apart my 180g and lifted it with the help of 4 friends) and stack the tanks one over the other so that the top runs to the middle then the middle to the bottom then to the sump which returns to the top again...have used this system in the past with 2 50g and a 40g sump...never had a problem.

Thought of stacking the tanks early on in the planning stages, but I really wanted to have all the fish and corals, etc. at an optimal viewing height. It will look much nicer in in this configuration after the stand is complete as well.