I put in a home machined one modelled roughly on the Andair version. The reservoir retains about 1/2 cup, mostly water and is integral with the unit... Works great. Only grey exhaust on the belly... I would NEVER put the yuck it collects back into the engine...
The breather from the engine enters the separator axially like a cyclone, and exits the unit centre top to discharge over the exhaust per Van's instruction...
I empty the cup about 3x per year... YMMV