Originally Posted by 
Tote
				
			 
			The valve assembly screws out to let the water out. Jack the tractor up, rotate the valve to the bottom, pump up the tyre and remove the valve assembly and the tyre will empty itself. If you are not ploughing anything I would be tempted to leave the water out after its fixed anyway, easier on the drivetrain that way if you don't need the traction.
Refilling with water is done with a fitting that connects to a garden hose and lets air out when filling. Jack up the wheel, set the valve to two o'clock, fill with water and pump the remaining space up as you would a normal tyre.
Fittings are available from your local rural tyre repairer. My bet is that you have hit a rock with your slasher and it has hit the rear tyre, the give away is if the leaky tyre is the one in line with the rotation of the slasher blades (usually the right hand one).
Regards,
Tote