Grey Tank Odor

We were having the same problem which we solved by cracking a window some when we ran the Fantastic fan. The fan has to get make up air for what it exhausts and I feel it was sucking the outside air down the grey water tank vent line and then past the water in the p- traps. I also started putting black tank chemical into the grey tank. Haven't had any more problems since we started doing the window and chemical.

We have two grey water tanks, one for the bathroom and one for the kitchen sink. Only the bathroom one vents through the roof. The kitchen one vents through the side wall behind he sink area. This was the main culprit I believe.