The main drain in my house is backing up. I had a plumber come in and clear the main drain and after a month the problem came right back. Is there anything that I can do to fix this besides call in another plumber? Does an old house (approx 100 yrs) have a main drain and a trap or is my main drain a trap? There is a box in the floor with tow pipes and this is where the water is coming up from. Please help, I'm a new homeowner that going crazy.