There is a way to remove the tank without an oil purge, but you need to be careful and not lose any oil out of the oil lines especially the oil outlet line to the engine. You can remove the line off the tank and before any oil comes out plug it so it stays full. Do it to the outlet line too. These lines must stay full of oil. If your not sure how to protect the oil system from air introduction then it should not be done.
If you loosen the tank top and lower the tank away from the top and oil tubes (assuming you have the clearance to do so) while maintaining the elevation of the tank top relative to the engine, you should be able to clean and reinstall the tank and not have to do a purge. The oil hydraulics of what I just described is the same as draining the oil from the tank which does not require a purge. Make sense?