moth balls in the petrol tank - Guinea pig

[Kryton]

well the time has come to try it for myself. :
ive got a full tank of fuel so now i just need to know how much i should put in.
i believe that im getting Napthalene Flakes (instead of moth balls) but wont know for sure till the other half gets home from shopping.
should i try and made it as powdery as possible or will it just disolve anyway?
will keep an updated post of what happens over the next week.