I have a basement sump for my basement bathroom. It pumps up about 4'
to the main drain that goes out to my septic. We just bought the house
and I need to put a backflow check valve in it. How far between the
sump and the elbow that goes out should I put the valve? Does it
really matter? Didn't know if it should be down closer to the sump, up
where it goes out, in the middle, etc.?

Thx!