If it's the Carver/Truma crystal filter that fits in housing of water inlet any caravan spares shops will sell them around £7. Tip for easy removal cut slot in end of block of 2x2 timber to fit the turn plate on the filter drill hole in block opposite end through side for T handle I made one and boy is it easier to replace filter.
These should be changed annually and not left in place during storage over winter remove the filter and pop off the clear top and screw it finger tight back in to filter housing to close off the opening.
And in case you forget drain toilet tank and water heater tanks before storing for winter even if under cover.
Bob, November 2009
