I'd think so too -- but every oil change business around here uses
a pump now instead of removing the drain plug. Apparently the
practice hasn't caused any damage.

Ted B. wrote:
Also, the main
reason to change the oil of any engine is to remove impurities that
accumulate in the oil (some of which are heavier than the oil, so they are
pulled down by gravity). I would think that draining the oil with gravity
would be more likely to get these impurities out than sucking the oil out
through the top of the engine. Right???