Being European I do my oil change once a year and since the oil disposal location is on the same street as my local garage, I need to drive there anyway so no time lost there. And as I'm working and making money in the lobby while waiting for my car to be ready, I count that as a zero loss.

You might not find it messy, but I do. I don't like doing it. And it costs me the same amount of time and money if I have my mechanic do it, so that is why I outsource it.