The way I clean oil bath cleaners, although it might not be the best possible way to do it, is:
1. Pull the bottom bowl off
2. Depending on the style, there may be removable screens stacked on top of each other. Separate them and clean them with brake cleaner or other similar product.
3. Dump out old oil and clean any sediment out of the bowl.
4. If theres other baffles in the housing that arent removable, just spray some cleaner in there and let it drip out.
5. Finally, reassemble with fresh oil