I have raw water cooled engines, so every year I have to deal with the drain plugs. Well, I probably don't REALLY need to, if I wanted to flush enough coolant through there to make sure the blocks got enough. However, I always do. I used to put the antifreeze in first, then pull all the plugs out and recover most of it, but it would also let me know how much antifreeze made it to various parts of the engine and manifolds. Then, I migrated to pulling the plugs first, draining the water, then putting them back in and running the antifreeze through.

The 'outside' plugs on the block are hardest to get to. The fuel tanks are outboard of the engines, so to get to these plugs you have to lean over the engine and reach down and 'feel' for where the plug is and unscrew it blindly.

So, this year I changed the plugs out for hose barbs, and ran a hose between them. I put a hose-barb splice in the middle. To drain the block all you have to do is pull the splice apart, which is right near the front of the engine and both sides drain. Because I used a straight hose barb on each side, you can run a coat hanger or other flexible wire up the hose to make sure nothing (like rust) is plugging it and preventing any draining. It's also so much easier to re-capture if I need to... just put the hose ends in a bucket or tub.