Best way to sand off metal burs from inside genesis top cap

[gokusnimbus]

My DID's top cap has metal burs on the inside of the stock airhole and it catches juice when the condensation builds up. theres enough juice around the airhole to interrupt the airflow when i take a drag. it sounds like a runny snotty nose. What's the best and cleanest way to remove the burs w/o damaging anything else?

 

[WattWick]

I use a small round or oval file.

 

[pron72]

I use a dremmel tool with a wire brush. Works great.

 

[E_DeCastro]

sand paper?