Can make a complete kit for around £30.
You can use anything as a receiver of the pressure, vent the top of this to atmosphere, and the lowest point as the return, fill the canister/receiver with SCRUB BUDS, these are SS but packed well in there have a huge surface area to allow oil mist to get caught up and drop down to the return pipe.
The canister/receiver can be anything you want a box a tube etc and weld on the pipe stubs, can even leave something with a removable lid so you can clean it out if wanted.
Look on www.ratsport.co.uk for some good cheap bits as well.
tabetha