Hi Dave,
I'm not sure if it's the "approved" method (or even a good idea!) but I put mine in a suitably sized jam-jar with a good tight fitting lid about 1/4 full of petrol & shook it. Repeated until petrol stayed clean..! Allow to dry & replace in tank..
Make sure the jar is not much longer than the filter - stops it moving too far & smashing it's way out!!
Cheers,
Adrian