Montana 1000

[Kurt]

Paul.

Please take a little advice from your retired plumber friend.

Sewer back flow preventers are not 100% reliable but you can do something that will help before pulling put like you do for extended time.
If that preventer was installed properly you should have access to the devices cleanout cover in the basement floor or pit. Open the device and make sure that there are no obstructions like solids or paper holding the gate open before leaving home. I have been called to many homes where the device has failed because of this reason.
The only safe sure way to stop backup is installing a gate valve and shut it before leaving home.
But this also can cause a problem with homes with basements with out sump pumps to take care of surface or ground water leaking into the basement to pump the water back outside or water line breaking if it was not shut off before leaving where the floor drain will not be open because the gate valve is closed.

Kurt