<<Changing the engine oil and the filter on the TSIO550E
 engine can be a real mess.  Can anyone make a recommendation on a quick
 drain retrofit kit for the drain plug?>>

Here's a system I always used on my sailboat engines, whose oil is even more
difficult to change if you can believe that:  Install a "T" someplace in an
oil pressure line and put a small shut-off valve in it.  Hook up a hose to
the valve (the valve is in an easy place to get to or leave the small drain
hose in place).  Start the engine an open the valve a little in order to let
a small stream of oil out.  When the oil pressure drops shut the engine off
and you're done.  No damage to the engine unless you forget and don't notice
the oil pressure dropping.  I fall short of recommending it for an aircraft
engine because of the prop spinning, blowing things around while the oil is
draining.  And, no it doesn't drain quite as much oil as from the drain plug
and you are still stuck with a full filter.  Like I say, I'm not
recommending it, just putting it out there as another alternative.

Gary Casey