Water (fresh, black, and gray) has been our limitations. We are 50 gallons fresh, 36 gallons gray same size for black. Not so much fresh in that fresh water anywhere in gallon jugs on up etc. We also have a freshwater bladder that we have used for extended stays. It’s grey and black and we must watch. As far as black goes we tried and gave up with the composition toilet. It did not work out for us. Never got far enough with the composition toilet to try the combination of gray and black tanks. Even when “allowed,” we do not dump our gray on the ground. If the stay is long enough, we use the macerator pump into our 42-gallon Tote along and take it to the proper facility and refill the freshwater bladder.