I have a basement bathroom that requires a pit and ejector pump to move the waste up to the septic line. The check valve makes a loud bang when it closes, and I've been thinking about replacing it with a different model that hopefully wouldn't bang so bad.

However, in looking at the plumbing I'm not sure why the check valve is there. After the check valve, the pvc continues vertical to a point that is about 8-10 inches higher than the septic drain line, then joins the the septic drain at a 45 degree angle. It seems to me that with the ejector piping being actually higher than the septic drain line, there is no chance of sewage having a reverse flow into the ejector line. Why is the check valve needed?

Any comments on this would be greatly appreciated.