We own a 1996 dbl wide mobile home, a few weeks ago the master bath started draining slowly.When the bath water is released there are large air bubbles in the toilet, and when the toilet is plunged water comes up in the sink. I took a small 1/4" snake on the roof vent and could only get to floor level with it before it hit something and wouldn't go any farther. A plumber came out pulled the toilet and snaked the line, that helped some, but not great, he then pulled the trap vent off the sink piping and everything works o.k., he said to buy a new trap vent, we did and it is back to the same thing.Works fine with it removed . Is my roof vent plugged and if so how do I clear it, I have heard of running a garden hose down it but the temps are below zero and I'm afraid I'll fill the vent pipe with water and it will freeze.