I do like the air nozzle idea. I haven't looked closely so I don't know if a piece of small tubing could be snaked in through the bulb socket hole. If so, most things could be vacuumed out. I have a feeling, though, that there is no opening between the bulb socket holes and the rearward areas of the tail lights.

 

I had a spair set of tails with dust in them, I filled them with hot soapy water, let the water run into the lenses then shook them around until they were clean. Then rinse with clean water, fill them up and drain them out.

Let them sit for a couple days or force dry them in an oven at 150 deg for a couple hours.

This wont work for spiders


Also, I tried using compressed air, it didnt do anything.

 

^ about to post that same thing.

Just be careful, the reflective surface may not take much.