The guy who installed our water tank with connected pump years ago didnt fit the stop valve inside the tank..Q: can i add a normal ball valve on the pipe between the tank and the pump,or it wouldnt work? Idea is to fill up the water in the evening with the valve closed,and then open it in the morning for use...like now the water thats left in the tank at the end of the day is gone in the morning...and we have slow water supply..