My washer smells like sewer after I use it .It doesn't happen immediatly just a day or so after . I cut a hole in the wall and it feels like the p trap is empty. i tap on it and it sounds hollow. Can there be somthing in it and it is soaking up the water? Or is the a possible vent issue.You can't see anything in the vent on the roof ,but that doesn't mean there isn't something in further down.What do I do now?