You know your colleagues and their working habits – choose a dunk-it! that you know will appeal to them and plan it for a time when they will find it easy to support you.
Get the bosses involved – everyone will turn up to see them dressed as serving wenches or being dunked with wet sponges.
Involve the sports and social club – they will certainly be able to give you a steer on what has worked well in the past and may be willing to join forces.
Piggy back – do you already have an event planned to which you could add a dunk-it! theme? A family fun day, a barbecue or a summer ball would all lend themselves to the dunk-it! treatment.
Matched Giving – many employers encourage their staff to get involved in good causes by operating a matched giving scheme. Yours could be one of them, it's well worth finding out.