I'm guessing that you have a manifold with the individual tank shut off valves located in a settee. In our 36 MK II, it is located near the freshwater pump. Ours is difficult to find or access because its buried beneath the AC duct work.

I had the same problem. The change-over valve was in a very awkward place to reach and definitely not convenient.

Someone else posted this years ago with a full description on the changeover so maybe they will see this and jump in, but what I did was remove the fire extinguisher from the slot/shelf under the stove (before anyone freaks, I moved the extinguisher to a hanger right inside the aft cabin door) and insert 3 valves (one for each tank) in that position. I can now switch tanks easily from right in the galley without having to root around under drawers under the sink. Very worthwhile change.

Chuck Parker