I've owned my MPG 183 for 14 months. Month 12, 4th use, a foul sulphur odor started emitting from the sink drains. I was told by the vendor that I needed to put chemicals in the gray water tank. I am doing so, and it has helped. I'm also flushing the fresh water/gray water tanks repeatedly to try to clean it out. When I read the manual there is a mention of the p-traps being in place to prevent odor from coming up. Is there a chance that the p-traps are not working? How would that be determined?