Spray with clean water with nothing in it! You can use your hose, but don't add anything (being able to shoot a stream of RO filtered or distilled water would be better - a Super Soaker can help you here.)
Flush with either elecrtical contact cleaner or good brake cleaner. Please, for the love of Gawd and all that's holy - do not RPT not use WD-40! It is not a contact cleaner, and leaves a film on parts ("WD" stands for "Water Displacer" - that's what it's for. It's good for preserving metal that you're storing and for helping to remove labels - but that's about it. One can of WD usually lasts me five years or so...)
Flush again with clean water. You can smack the thing about if you need to do so to dislodge anything in there. The front (drive end) bearing should be a sealed assembly, I'm not sure about the rear. Some are open.
If you are so inclined, you can just remove the thing, split the case, then flush out the bearings and the brush holders - then re-assemble. Some light moly grease if the rear bearing is open will help, and the brushes can be touched up with 600 or 800 grit crocus or emery if you need to. Nothing coarser - you're just cleaning up, not removing material.