i bought a jetski sold as is not in running condition i noticed there wasnt a pressure regulator on the waterbox. i bought one and looking at it i notice there are 4 holes. one to screw it on from the bottom and two on one side obviously for water lines and then theres another one on the other side that appears to have threads or something and i can't seem to figure out where it goes. is it jsut a vent for air or something?