dripping extractor fan?

Could be:
1)Steam condensing on the inside of the vent pipe or hose. This steam becomes water as it cools and drips down through the fan. Could be reduced by lagging the vent pipe with loft insulation or similar.
2)Rainwater entering the vent pipe from the external grille. This may be wind blown rain if the fan does not have a backdraught shutter.
Either is particularly likley if the vent hose rises on it's way to the outside grille. The only soultion may be to re-route the vent pipe so that it falls rather than rises. Introducing a water trap may help if it can evaporate quicker than it builds up. Otherwise some form of drain may be needed.

Steve
November 2009