Before cutting the pipe did you try a pipe snake? If you cut the pipe and the clog isn't there, then what? Are you going to dig up the pipe?I’m hoping the snail didn’t get to far because there’s pipes underground but I’m assuming it got stuck early in an elbow
You said you inherited this setup, did it come with the house? Who buried the pipe?
You could have an air lock if the pipe drains underground then comes back up into your sump.

and if o had a snake in hand…for sure
