Facts are clear. appliance in basement (washer) when trying to eject water after a couple of minutes said water starts backing up into BATHTUB which is 8 feet higher than where appliance in basement is.
So water moved UPHILL. If there was a clog in pipe downstream then of course the water would back up to least resistance opening (the bathtub). If the drain downline was clear, but the vent in attic was clogged can the negative air pressure actually pull the water upstream?
Yes the toilet gurgles too, but that could come just from air coming back from the clog.
i'm inclined to think its a clog downstream and not just a vent clog.