Remove the belly pan and pull the lower hose. (drained) Flushing is dependent on why, if it is full of oil then I use Calgon (dishwasher) soap if I can find it, Premix it in a pail add it to the cooling system top off with water run to temp, repeat until oil residue is gone then straight water until detergent is gone. If your flushing due to scaling then I use Fleetguard cooling system cleaner from Cummins, follow the instructions and confirm use on a Two stroke.(Flushed). After all the flushing you will have figured out the best way to refill. I did see some 10 year extended life coolant available if that interests you at all.