The SureDrain is this thing from Fram:

Suredrain valve (http://rustysoffroad.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=FRAM-SD&Category_Code=)

It was designed for an oil pan, but they have one that is the same exact thread as our coolant drain plugs in the engine block of M54 type engines.

I was thinking this would make draining the coolant from the block a lot cleaner.

Anyone tried this? What do you think of the idea?

but squeezing through to get the tube to the engine block next to the headers is still quite a feat

I think the O2 will still be in the way.

I think the O2 will still be in the way.

i think that depends on the engine... the M52TU and M54 motors have their pre-cat O2 sensors on the top side of the exhaust manifold.

Not sure it would work because the water is under pressure at temperature. The Sure Drain was designed for oil pans which are not really pressurized.