[prairieschooner]

Be careful using a wire from a coat hanger it could do damage to the seals on the valve. That is why I suggested a snake or the water pressure. Richard could be right about the valve not being open though, if you had to pry it the handle could have come out of the gate (this is a Gate type Valve).
At any rate good luck, starting to sound more like RV. I would agree with your earlier post;
1st) Chemical..why not just may take a while.
2nd) Pressure.. OK I'd rather use Hydraulic than Pneumatic but the principal is the same, just air is more compressible making the pressure not dissipate as quickly as with water pressure.
3rd) The Snake.. you should only need on a couple of feet long. This method would require that you go somewhere that it wouldn't matter if you have a spill (visions of RV!). The last time I was in Elk Grove that would only be a few minutes drive but I am sure that has changed.
Good Luck