Exterior and Body

hi there,

i've seen foreman taking off this one screw on top of the thermostat housing flushing the radiator. what is this screw for? if i loosen this does it force water to flow through the thermostat without having to wait for it to warm up? i tried opening this screwn and when i start up my engine water came out... i dont have a gasket leak...or is this normal? i'm worried..please help out tq.