I'll ask Waste to look, if he has a chance -- he's done about 100 times more liners than I have. BUT . . . to just get those returns, I'd get them to do it. You can get the digging down down, and expose the piping on the back sides, but let them remove and replace the returns.

That way, there's no question about the warranty 3 years from now. (Hopefully, you won't need it, though.)