4 weeks ago we purchased a home that was built in 1971 and has sat vacant for the last 1-1 1/2 years. After about 3 days the shower in master bath started backing up every time we take a shower. The toilet will begin to gurgle and then water starts coming up into the shower. We finally had a plumber out to snake the drain for $155. A few days later the other bathroom did almost the same thing except water was coming up from the floor aroung the base of the toilet. Out came a plumber and he snaked from the outside pipe and from the roof vent for $185. Well, here it is not even a full week out and both are doing it again. We do have a septic, but we believe it was vacuumed approx 2 yrs ago per the previous homeowner. And of course no one has said there were previous plumbing issues. What could the problem be? The house was replumbed inside approx 2yrs ago, but not the plumbing under the house.