With enough hose and extension cords. Barn is not too from the house where the electric and water is.

Really would like to keep the tank in place. The thing is buried. The steering wheel, throttle handle, choke, gauge cluster, then all the sheet metal surrounding it has to come off.
Looks like quite the chore to get it out.

It's a project to get the tank out, pretty much the first thing installed.

Get a clean garbage can.
Run a hose from the drain on the tank into the can.
Toss in a sump pump, fill the can with some water and simple green and run the outlet of the pump into the fill cap of the tank.

Run that for a bit and let it circulate.
Flush it out with clean water and set up a work light right above it to help heat it up and get it dried out.

You will want to have the drain ready to install and the tank filled with fuel so it doesn't start to rust and create more problems.