Shop manual does not specify draining the block, only the radiator.
There is a cut-out opening in the underbody cover underneath the radiator. Reach through to turn the drain plug and allow coolant to drain into a catch pan. Crack the radiator cap to enable venting.
Remove/clean the reservoir and refill radiaotor and reservoir w/ fresh mixed antifreeze coolant.
Start engine w/ radiator cap loosely and warm engine (fans come on). Turn off engine, check coolant level, top up, and tighten radiator cap.
See you down the ROW
2005 Toyota Matrix
2003 Acura MDX
2006 Acura TSX
2010 Acura TSX