Having problems with the water not filling up the tank on my toilet. it is built in to cupboards and don't know what type it is. It has vertical pipe on the right, the ball cock is a small plastic square on the top of a screwed rod with an arm at the top which lifts with the water level. At the side of that is a large knurled nut which is allowing water to spray out. The water should come in at the bottom of the pipe but doesn't. Help....