Air compressor. I use cans of compress air, which air is getting expensive, so I am looking at a air duster on Amazon. Battery powered. Or getting the right hoses and fitments for the air compressor in my shed which has been rarely used.
I also use blue shop towels, micro fiber towels. Old tooth brushes and small paint brushes to get in the hard to reach spots.
How else do I take care of my RCs? Shock oil, and diff oil changes / rebuilds. And re-grease things up. And mainly keep the cars clean. I also resolder stuff if I did a poor job before (I'm getting there, still learning how to solder) Also making sure my batteries are in healthy condition. Measuring Internal Resistance, making sure cells are balanced and cells are not to puffy. I got a few batteries getting there so Ill be running them in my bashers until they need to go, as I do not want to take risks of loosing a battery or anything worse.
@bill_delong does a great job on taking care of his cars. Pretty sure he has a post somewhere on how he keeps his cars maintained.
For me it depends on the type of dirty. I will probably try to get most of the heavy dirt off immediately. I will then let the truck sit for a day and let things dry off and I'll hit it with a brush or compressed air. I just picked up an 3 gallon compressor from Harbor freight for $60
I have a form that I mark/fill in to record each run my RCs make. After 12 runs I do shock, and bearing cleaning/rebuild/relube general maintenance. After 24 runs I will also do ball diff rebuilds. My RCs with gear diffs, those diffs will get rebuilt every 36 runs.
(I gotta update spreadsheet)
Pre-run checklist includes looking for loose links/joints, wheel nuts being tight, and spraying CV joints with a dry lube. Post-run checklist: I normally do a quick look for anything missing, broke, bent, unglued, or leaking as I'm blowing dust/dirt off. Some of my RCs have their own personality and their own problem areas that need special attention before & after a hard run... like pillow ball suspension inspections
Cleaning... Indoor/outdoor RCing... racer/basher... a person will find their own method to keeping their RCs clean, and to a cleanliness level they are comfortable with. A full-blown tear down/cleaning (so clean you can eat off of it)/rebuild only gets done after running in mud, or I'm feeling super awesome that day. YMMV.