1998 U-320 with no slides.<br/><br/>I am trying to replace the Oatey in-line cheater vent/air admittance valves in our coach, but they won't budge by hand! I don't want to break any pipes. My wife's comment is, "I'd rather live with smell than delay the trip because you have to repair something."<br/><br/>Does the bottom threaded piece stay in the pipe stack meaning that you unscrew the...