where should I locate my return pump?

Hello, I have a mag 250 pump in a 10 gal sump that I'm about to hook up and wonder if I can just sit it on the bottom of the tank of need to put it up higher in case the overflow fails. It's about 4" high and even when I put a clay pot as a base in there (5"high) that was putting the pump pretty close to the top of the tank but only prevents 5 gallons coming out.
Thanks!

 

The return pump should be at the bottom of your sump. To prevent backflow you should have a siphon break in your return pipe. Just drill a small hole right below your water level of the display tank in the return tube.

 

Yea, sit it on the bottom. You'll want to do this too because the lower it is, the more evaporation it will take before the pum runs the risk of running dry. If you have an ATO, it should be that big of a deal, but it's better safe then sorry. Have you installed any baffles in the sump? Or is it all open?

 

Backsiphonage is from your returns or overflow if either or both are too low. The placement of the return pump has nothing to do with this.
To prevent backflow you need an air gap. never rely on check valves or drilled holes, both require maintenance and can still fail the moment you turn your back. All it takes is a flake of food, a snail, some algae. an anemone or fishe, even a single grain ofsand in the case of a check valve since it doesn't have to be a catsatrophis failure, even a trickle will cause a flood in time.
Make sure you have a properly designed overflow box and your returns are close to the surface so in a power outage only asmall easily calculated amount of water is siphoned back until the return is exposed to atmosphere, there is no better device than an air gap. No maintenance and nothing to fail. Always maintain enough room in your sump to contain that inch or whatever it is and you wil never have a flood.

 

Yeah, that hole in the line will work ok. And I'm going to buy a big shallow rubbermaid tub to put the tank stand in so if anything overflows it will catch there. I can put tank stuff like nets etc in there too. I mean my skimmer is a hang on back type plus the eshopps I've got a good chance of getting some overflow one day and the very idea of stinky saltwater all over my carpet is unacceptable. They have ones storage under the bed that are pretty shallow.