This sounds like a septic problem. Have a plumber ream main drain line from the house to the septic. Then if the problem still exists... Pull the lid on the septic tank and comfirm the waste water is entering the tank. Then, check the baffle in the tank for any obstructions. Depending on the age of the septic system there may be a ditrabution box in the leach field. this box can also get plugged but if so it ussually points to leach bed failure, which leads to a costly repair.Good Luck
