Nicholas has said it all really but the recommeded cleaner for ALL parts which have had contact with fuel is Methanol.
A certficate of compliance is also recommended and if Davie Mathews is reading this perhaps he can give us the benefit of his research.
Problem is, if you seal all tanks etc the diff pressure of 8,5 psi in the cabin couild cause damage.
The only problem I have had is with BA at Orlando airport, (no problem at Sydney or Bangkok for the WJM) even though the operating Captain was happy ( my F4 had one ounce of residual fuel in the hopper, the 747 had 80 tons of the stuff on board) to carry my F4 the station manager insisted it go cargo the following day, and several hundred dollars paid for air cargo ! Even the cargo agents didnt see the problem. Virgin, by the way are great Having said all that I am about to find out any problems with Qantas and AA when I leave for Florida Jets on Monday with brand new BobCat which has never been fuelled.

My experience with customs in Sydney is that they are very happy to attch a paper seal to the model for easy re-entry without any customs hassle. Good luck.