Ours is 40 gallons. does DW and I fine for 5 days of camping. Bigger thing for us is grey capacity. we have 64 gallons of grey, 32 black. with that combo a 2 week dry camping is fine. Usually where ever we go we either have access to fill our 7.5 gallon fresh water containers to refill the fresh, or carry an extra 30 gallons in 4 of them in the truck bed. I have a extra pump in the pass through with a siphon tube on the inlet and outlet plumbed into the fresh tank so I just stick the dip tube into the container, turn on the pump and wait a few minutes to get 7.5 gallons in the fresh tank. Sure beats lifting that bugger and using a funnel.