[twindman]

I had a similar problem. Went on for several weeks this summer - I just kept switching the full tank to one side, or so I thought. Anyway, it got to where neither side worked. So I read up on stuff and took both tanks out and dropped them about 3-4 inches on hard ground or cement. Also put them on their side and swished them back and forth. Both tanks then worked! Somehow both internal valves in the tanks got hung up.
p.s. I was about ready to buy a auto-crossover valve thing and try it.