I do have a leak in my bathroom toilet sink. when we use the shower at the bathroom upstairs, water leaks downstairs under the basement of the toilet seat/sink. It is kind of wierd. Everything else is good, no leak. But when we use the shower upstairs the leaks comes out at the base of the toilet seat. sometime also when we flush the upstairs toilet, the toilet downstairs shows some bubbles in the toilet sink/seat in the water. Any one who can help me would be very much appreciated. Thank you