I would like to know every once in a while my drain under the stationary tub back ups and the water from the washing machine ends up on the basement floor, the city comes out and snakes the main drain and everything is ok for maybe 4 months then it happens again what is causing this to happen? I keep a nylon on the hose from the washing machine to catch the lint and change it all the time. We do have big trees out front, but we also have the city come out every 6months to clean the drains.