Not for keeping the plane clean, but, for what it's worth...

Since the 70's automotive race engines have been using crankcase scavenging to increase HP. By creating a vacuum in the crankcase one reduces the aerodynamic forces acting to slow down the crankshaft counterweights, rod ends, etc., with the resultant HP boost. The key to this is to have the crankcase ventilation entering the exhaust stream in such a way that the exhaust stream is strongly pulling the crankcase vapors out, and this is accomplished by a properly shaped tube directly in the exhaust stream. I don't believe that this sort of scavenging can be accomplished by simpy having a nipple like is used for using exhaust pressurization of the fuel tank. The tube in the exhaust stream needs to actually create a vacuum using the flow of the exhaust.

Another method to reduce parasitic loses in the crankcase on the race engines that we used was a crankshaft scraper. This is a piece of metal that was shaped such that it would be within about 0.005" of the rotating crankshaft compnents, including the counterweights, journals, etc.. It was mounted on the interface between the engine block and the oil pan/crankcase and angled such that the oil was scraped off as the crankshaft rotated. Slow motion photography through a clear plexiglass oil pan was able to quite easily show the benefits. Without the scraper there was as much as a quart of engine oil resident on the crankshaft (from the oil coming out of the journals) and this is the mass that was scraped off resulting in less rotating mass and the resultant increased acceleration and HP. Obviously there are many differences that would keep this from being applied to our little engines, but it was first used on full scale aircraft engines. When the DC-3 was being certified it was to have been able to take off in a specified distance (I seem to recall 1000') but the first flights weren't able to do so. A couple of engine engineers took the engines back and developed the scrapers and the result was a 10% reduction in take off distance - more than enough to certify the plane.