I got it figured how to vent the fresh water tank.
Not sure how to vent the gray water on the truck. In a house there is a cesspool vent when the line reaches the house. Then the drain pipe has a vent to the roof.
Will there just being a vent on the gray tank be enough? The tanks are only going to be 5' from the sinks.
Told my son that there has to be traps from the sinks to keep air/smell rising up the drain from the holding tank.
Is there anything I am leaving out?
Thank you to all that have helped.