When we lived in Germany and I worked in the passenger terminal, we adopted a male guinea pig after a passenger came to check in for a flight and was unaware we only accepted dogs and cats for air travel. I ended up bringing the little guy home and we called him Mugatu. He lived as a single pig on shaving for bedding in a fairly decent size cage, although knowing what I know now it was probably too small for him. I've learned a lot since then. Mugatu needed fairly frequent boar cleanings. Smegma and whatnot really built up with him, probably due in part to the bedding and he was fairly sedentary. I'd say I probably cleaned a large lump out of him every 3-4 days and he could have done with even more frequent cleanings.
At present we have three boars, two of which are roughly 6 or so months old and one who is 3 years. They are all bedded on fleece, currently in a 2x4 C&C cage. When I do my weekly thorough cage cleaning they all get checked and if it looks like they need to be cleaned out then I take a q-tip with a bit of mineral oil to them. I know some people don't feel that mineral oil is a good thing to use, but I don't think they'd appreciate a dry q-tip swished around their bits. If they look clean, I leave them be. One of the babies, Star-Lord is a bum dragger, the oldest pig, Gus, is fairly sedentary.