Class A Customs 18 Gallon Fresh or Gray Water Holding Tank rv Concession Trailer T-1800 18 Gallon Capacity Fresh / Gray Water Holding Tank by Class A Customs NSF / FDA Certified Material - Fresh, Drinking Water Safe WATER TANK MEASUREMENTS: 23 Longest Length (not including fittings) x 10 1/2 x 17 1/2 (rotate tank to change height or width) Average thickness 7/32 +/- (+/- .25" on each measurement) BUILT-IN FITTING: (TWO) 1 " Dia screw in balloon fitting (threaded female - NPT Standard) fitting will be closed, to use remove inner membrane with razor knife (TWO)  " Dia screw in fittings (threaded female - NPT Standard) NON-PRESSURIZED TANK: you will need to vent this tank to use it, letting air in and out during use. Do NOT hook garden hose to tank use a fill dish.