From there site:
Cleaning your filter:-
Using Petrol:
The best and cheapest way to clean your filter is to use normal petrol which is readily available. Using
a shallow, petrol resistant tray, fill with around 10mm depth of petrol. Dip the filter in the petrol and
agitate so that the petrol goes into the filter foam and draws the dirt/dust out into the tray. The petrol
will dissolve the oil instantly and will also help draw out the dust. Once you are happy that the entire oil
residue and dirt has been removed by the petrol dispose of the petrol in the appropriate manner (at a
recycling tip or similar but not down the household drain system). Only repeat this process with clean
petrol if necessary. Immediately refill the tray with cold water plus 5ml of washing up detergent and
agitate the filter in the solution for a couple of minutes. This process helps remove any remaining
oil/dust and also removes cleaning solution residue. Rinse the filter in cold water until none of the soap
suds remain and then shake the filter to remove excess water. Leave the filter to air dry in an open
environment, but away from any ignition source or naked flame for a minimum of 24 hours, then re oil
using instructions above.