[GTP Dad]

To answer part of your question, if you use regular antifreeze with the dex you will have issues. If you use the Prestone or other type of extended life antifreeze that is compatible then you won't have any problems.

As for keeping the sludge out change from dex cool to another brand of long life antifreeze and you shouldn't have any issues with the sludge. As for the drain plug I have never dealt with one in the way you describe so I can't give you any good advice.