FIRE UP wrote:

Ed9824V,
Quite a bit of the time, the manufacturers post all that information of fresh water tank size (gallons), holding tank sizes, propane tank and fuel tank size, GVWR and much more on a full size sheet of paper and glue it to a cabinet wall or door. Most of the time, at least in many rigs I've been in, it's been in the back or master bed room closet, on the inside of one of the closet doors. If it's not there, then look up archives of the model, and find possible brochures for that model and year.

Getting exact tank sizes and measurements for calculating gallon-age is sometimes fairly difficult due to the tanks being partially hidden, obscured by many obstacles, and, many that I've seen also have diminishing measurements or, they taper off due to the angle of mounting and where they dump into a dump valve. That makes for difficult and inaccurate calculations.

But, even when it's all said and done, if you've calculated that the fresh water tank is 80 gallons, by law, the two holding tanks MUST be able to contain all that gallon-age COMBINED! So, that means at the very least, you'd have two 40 gallon holding tanks. But, that's kind of rare. Much of the time, the manufacturer makes one just a bit larger than the other like in your case, one would be say, 38 gallons and the other, 42 gallons. Logically, the larger one would be the gray water because obviously, you'd use more of your fresh water for gray water accessories and less for potty use. But, that's not always the case. Sometimes the manufacturer does it opposite and makes the black water tank a bit bigger.

That's done due to various reasons like, convenience in location of the tanks etc or maybe even due to special order by the purchasing customer. Hope this helps some.
Scott

Ed9824v wrote:

Checked the bedroom closet door and found a lot of valuable information but not the tank capacities so will be doing a fill test thanks ED