Greetings all! We are new to the world of travel trailers having upgraded this year from a pop up. We have taken the new trailer on 3 weekend trips to state parks and just this past week stayed for the week on a full hook up site. We had not had any problems with odor coming from the tanks when we were not on a full hook up site. About mid-way through our week long stint a terrible stench, akin to rotten eggs, would emanate from our sink and tub drains when taking a shower and worse yet when emptying the bathtub. In addition, when dumping the tanks, there was no odor from the black water tank, but the rotten egg smell when we dumped the gray water. That being said my questions are: 1. How do we clean the gray tank? 2. How do we prevent this from happening again?