Oil Separator for Crank Case Vent Line

Aircraft engines don't use tightly fittet pistons as they are old air cooled designs with large temperature spread. Therefore there is a lot of blow-by past the cylinders ending in the crankcase. The stock solution is to use a 1 inch hose and just dump those fumes out the bottom of the engine compartment leading to oil and dirt accumulating on the bottom of the fuselage.
There are designs that separate the oil and return the oil into the oil sump and only dump the cleaned fumes out the bottom. Drawback is that not just oil condensates in the separator but also water and therefore water is returned back into the oil pan.
To further clean the remaining fumes coming out of the separator, some opt to feed them into the exhaust pipe. Because the exhaust is very hot, burnt residues build up at the adapter which need to be cleaned out at every oil change. To rule out clogging, it is necessary to also install a bypass valve that opens should the exhaust feed close up.
There are other designs that just use a reservoir to hold the separated oil / water for manual dump after the flight.

See also this FB Thread

Vendors providing oil separators for the crank case vent line

• AntiSplat
• Spruce