Our 1992 Breakaway has the water pump mounted below the sink at the lowest level of that cabinet. The Shur-Flo pump takes water from the fresh water tank and pressurizes it for the rest of the system. Immediately after the pump there is a "T" with a 90 degree elbow that routes down and through (2) 1/4 turn block valves. It looks to me that these are drains for the system. They are normally closed. My question is: Why are there 2 valves in series? The only thing I can imagine is for a double block to prevent accidental loss of pressure and water. I am probably all wet, no pun intended, and would like for someone to enlighten me about these two valves. I don't have a plumbing drawing.