I bought a vacuum oil pump to change the oil in the boat. First time I used it, pulled out the dip stick stuck it in, dunk dunk on the bottom of the sump pan and sucked away. In 10 minutes all the oil was out, no mess, no hot sump plug, no oil spills.
So it got me thinking, what is the best gadget you've got for your boat? Mike will probably say the sail bag/cover.
So what is the best device you've bought, what is the "Ducks Guts"?