Sounds like inadequate venting for the drain lines. Could have been build this way or maybe a clog has developed in the vent pipe. Such as birds or squrrels building a nest in the vent pipe up on the ... read more
We keep a spray bottle filled with the solution below on the counter and use it as needed. We apply sealer once a year.
•1/2 cup rubbing alcohol•2 cups water•8 drops dawn dish soap