Charles what model X5 do you have?
As for flushing fluid, if you are somewhere that it freezes stick to BMW Coolant mixed 50/50 with distilled water. If you're in a warmer climate consider yourself lucky and flush with distilled water the 1st time then on the final fill use a 50/50 mixture of BMW Coolant. I have the BMW coolant available
HERE.
James with ECS