The air idea is pretty good if you do it in a well by putting a small pipe down to the bottom and turn on the air it creates a bubble and pushes all the water out of the casing. You will get completely drenched if you locate the valve close to the well head don't ask me how I know that. If that doesn't work you can get a large lag bolt and weld it to the end of a metal pipe long enough to get to the bend in your standpipe then you can put it down and screw it into the material in the pipe and pull it out