Thanks Richard,
I've been draining as much as I can get out by putting a modified clothes washer hose on the spigot at the bottom of the radiator but I was thinking of flushing the system and so I need to get it all out.

I've been refreshing as much coolant as I can out on a yearly basis so I may not really need to do anything more unless I start to have problems.

I have to drain the system in my garage so that's why I was asking about the19mm drain plug.

Bud