Secondary tank for A.I. Injection. Basically, large suction line. Methanol/Water mix is stored in OEM windshield washer fluid tank. Tank modded for application. Level sensor, bung in bottom for suction line, etc.... Alum egg shaped tube holds approx. one qt. of fluid too which gives me an extra qt. even after low level sensor in washer fluid tank indicates low, and also ensures pump (on passenger side just below level of alum tube) cannot suck, the suction line dry.