grey tank backing up in tub
This last weekend out camping, we filled the grey tanks up pretty full. I have 2 grey tanks that are plumbed together. one is below kitchen sink, and another below shower. They connect together and drain in same place.
When I pulled the camper to the dump station, 1/2 mile away from camping area. When at the dump drained black tank and started to back fill black tank. While back filling black tank, the tub started to fill up with grey water. What would cause this? Grey tank in front when pulling pushed more water to the back grey tank and came up through tub drain?
Or vent problem, I think the back grey tank and black tank share the same vent.
Any help appreciated.