I basically disconnected the heater supply and upper radiator hoses and flushed through the cold engine and heater with a hose until the water was clean. Then I refilled the system with water and a flush and ran it for a few days. I then flushed it with a hose again, dumped a couple of gallons of demin water through the system to get rid of the tap water. I refilled with 50/50 mix of MB antifreeze and demin water, leaving the top hoses off as I filled. I ran the engine with the heater on and topped of the coolant as required. Keep an eye on the coolant level for a few days to make sure all the air is out of the system.

It was just difficult to get to the drain plug on my turbo, and I am told it takes quite a bit of torque to remove the drain plug. If you search this forum, you will find several discussions of the best way to flush. It probably is better to remove the drain plug, I just didn't want to deal with it at the time.