Just to add if using Milton be very careful if you have a steel sink as apparently Milton can leave a stain on the metal and this stain cannot be removed. We use Puriclean and sterilise the waste water and aquarolls about once a year. We only sterilise the caravan system once every 2 - 3 years as we don't drink water from it. As Damien has stated dump the filter and get on with enjoying yourself.