Both you and AR are correct about the need to siphon oil from the sumps of boat engines. My previous yacht had a Perkins engine with a built-in oil sump pump. Fast and clean. However Volvo bought Perkins and the current line of engines does not have a sump pump and I have to siphon oil out via the dipstick tube, using a vacuum extractor pump. Very slow and it only works when the engine is warm. I cannot speak for other makes of engines. As you can imagine, I do not change the oil quite so often.