Or you can just pull the motors every time like I do

Above is the best possible way. Many drain holes aren't big enough for a line. I just bring it up around the front of the motor and zip tie it to another line. You can see in this photo on the port motor it's zip tied up the left side of the front of the motor. The end is just to the left of the thermostat housing.

One word, Oilboy! Awesome and simple hand pump (easy) extractor.

Can be had from West Marine etc. for about $50.

Oh ya, I use a handpump with my application. Works great when pulling from the bottom of the pan. Rare possibility of leaving any gunk in there unlike pulling from the dipstick.

I bought all kinds of pumps that weren't worth a chit. I finally bought this one. It works great, and you'll be surprised at all the usages you'll find for it.

I resemble that, and its not funny anymore. I spent all weekend upside down changing a leaking oil cooler. Should have just pulled the motor as usual.

So how big of a hull drain plug do you need to have to successfully accomplish this?

Just the standard drain plug will work.