<a href=showthread.php?s=&postid=8193059#post8193059 target=_blank>Originally posted</a> by crumbletop
I don't use one on my tank. They are typically installed between the return pump and the bulkhead. The reason I don't use one is that they are unreliable if you are counting on them to stop back-flow and prevent flooding your sump. What I do is make sure there is enough room in the sump for the backflow water through the return lines when the return pump is switched off. If you do that, you won't need a check valve.