A line marker carries a spray nozzle assembly for marking or painting a line on a horizontal surface. The line marker has a hydraulic circuit which includes a reservoir for holding marking liquid therein and a tank for holding water therein. A pump can pump marking liquid through the spray nozzle during a marking mode of operation or water through the spray nozzle during a flush mode of operation. In the marking mode, at least some marking liquid is recirculated back through the reservoir to help keep the marking liquid in the reservoir agitated and mixed. In the flush mode, water is blocked from entering the reservoir and is recirculated back into the water flow from the tank. In the clean out mode, the hydraulic circuit is operated as if in the marking mode, except that the reservoir is rinsed with an external source of water with the rinse water circulating through the hydraulic circuit and back to the reservoir. At the reservoir, such rinse water is directly conducted by a hose through a drain outlet, thereby speeding the time needed for clean out by avoiding recontamination of the reservoir with rinse water that has already passed through the hydraulic circuit and which is carrying some marking liquid.