Occasionally my sink in the laundry room won't drain after washing the laundry, the house is old and some of the pipes underneath the sink are original to the house. I have replaced the elbow joint and lower piping with plastic piping, though. This is about the extent of my plumbing knowledge. Right now it won't drain and I've taken the elbow joint off to try to clear up the problem. I was able to drain the water that way but when I replace the pipe and try running the water again it backs up again. I have a metal strainer in the drain itself and have recently cleaned that out as well as underneath it. My husband thinks the pipes might be frozen as we have had a number of snow storms here is PA. Any thoughts on what to try to get it to drain again? Is there anything I can do to unfreeze a pipe if it is frozen? I'd rather exhaust all avenues before having to call an expensive plumber! Thanks!