You can use degreaser [aerated kero] and then wash out with a hose in water. Blow dry or air dry for a day or so, and 'viola, ze air filter she ez clean'. Do it all the time, they are made to be reused. Then you buy a priority brand air filter element oil and spray or tip approx. two tablespoons of oil onto the clean and dry filter and work it through the whole element. You should have nil excess. The oil is important, it traps the fine dust particles that the foam cannot filter out. Best hint is to clean the element regularly [<5000km]. If you have oil leaving the filter, you have used too much. The oil has to be throughout the filter, but not able to be squeezed out at all.
These same principle filters are used everywhere [motorcycles, dozers, scrapers, trucks, 4wd, and cars]. They are a good product and work extremely well however they are open to abuse and neglect. They do take some learning skills for the novice. They breath freely, filter very well, and give years of fault free low cost service. They DO NOT impede performance [they actually have superior breathing capability to many std filters].
Another reason for the filter being oiled is as a fire retardant for backfires etc, a non oiled filter will catch alight and burn [especially if there is fuel spitting back through the carby]. This reason is probably not so relevant for turbo vehicles, but is essential for motorcycles [i saw a m/c burn almost to the ground with a backfire and airfilter incident out on the roadside, no fire extinguisher, no water].
I run a HKS pod in the skyline, a foam Unifilter in the Hilux, a foam K&N in the TBS motorcycle, and a custom foam filter in my other TSS m/c [both road bikes], and they are all serviced and oiled as above with nil probs.