Grey/Black water tank?

Long time lurker.
I am converting a 24' into a car hauler / camper.I will have pictures up soon.it has all the kitchen and bathroom up in the front and removable beds in the rear.I have it setup to sleep 4 comfortable.
What have you all done for a portable tank?My 3" outlet is only 11" off the ground and most 30+ gallon portable tanks are 14" tall.
I am converting a 24' into a car hauler / camper.I will have pictures up soon.it has all the kitchen and bathroom up in the front and removable beds in the rear.I have it setup to sleep 4 comfortable.
What have you all done for a portable tank?My 3" outlet is only 11" off the ground and most 30+ gallon portable tanks are 14" tall.