Well for the trapped dirt part, this is how I did it. I heated up a 1.5mm drill bit, poked it through the rubber layer of the tire. Find an unused servo eyelet/bushing, and fit it in the hole
Shake off the trapped dirt inside. Remove the eyelet when done (well of course you do)
The dirt is bluish because the foams are blue
As for my 2nd problem....I plan to freeze the tires so the CA will just shatter once force is applied. Will update you guys