If there is only one valve I would think it would have to manage both lines; input and output. In one position it allows water into the tank and water out of the tank. In the other position it would close off the output from the tank and direct the input straight to the output. So both lines would be going through that valve. Is that what it looks like, two water lines going to the valve?
Rich & Yvonne
2006 Safari SE -Dora-
2004 4Runner SE
Most of us don't know exactly what we want, but we're pretty sure we don't have it. -Alfred E. Neuman