According to my manual, the '76 31' center bath capacities are: Main Holding tank (Int'l) 23 gal Aux holding tank (Int'l 16 gal Main holding tank (LY) 13 gal Aux holding tank (LY) 10 gal Water tank (Int'l & LY) 50 gal Rear bath models are 20 gal for main tank, 14 gal for aux, and 50 gal water. Bob Hightower '76 Sov #11365