Abstract: A spraying system for providing a pressurized liquid spray for cleaning purposes is mounted on a vehicle for use outdoors. The system includes a liquid storage tank, a spray device for directing a spray of liquid therefrom, and a liquid supply system for pumping liquid from the liquid storage tank and for providing such liquid under pressure to the spray device. A standpipe is located within the liquid storage tank, connected to the tank liquid outlet, having a liquid inlet spaced above the level of the tank liquid outlet by a short distance. As the liquid is drawn from the tank and eventually reaches the level of the standpipe liquid inlet, air will be entrained with the liquid as the liquid then continues to enter the standpipe, causing the spray to sputter or spit as it exits the spray device. This alerts the operator to a low level of liquid in the tank and comprises a warning that use of the spraying system should be discontinued until the liquid storage tank is refilled with liquid.