I don't know if this applies to all Volvo Penta engines, but I just discovered that the oil suck-out pipe does not reach the bottom of the sump on my MD22. Last time I changed the oil I noticed that the oil on the dipstick was not clean. This year I bought a 1m length of PVC tubing to fit inside the suck-out pipe. I emptied the oil as normal, then pushed the smaller tube in until it stopped, I got out at least another 500ml.
Next time I'm going to try a more rigid tube, and a more permanent join to my pump. An 8mm drill bit fits quite loosely in the pipe.
Some of you may already know this, but I thought it was worth a mention as the VP manual shows a pump attached directly to the pipe.
For a related question regarding the dipstick, see
this poll.