Changing drive oil
 

Do I need to warm up drives before draining oil? If so, whats the best way to do it while the boats out of the water?

It is not neccesary, hot oil would however drain quicker. I think it would be difficult to get the oil hot enough to make a significant difference without load.

it also suspends trash in lube when drained.

No need to warm it up. Pick a warm day and allow plenty of time for it to fully drain.