Hidonlo, I can only go by what my 25-foot 2009 Hi-Lo had specified when it came from the factory, which was a 30-gallon fresh water tank, a 32-gallon gray water tank, and a 30-gallon back water tank. However, when dear husband sanitizes the fresh water tank each year before the start of the camping season, he said it only took 28 gallons before overflowing.
Dee
Summerville, SC