Hi and welcome to the wiki and forum.
Is you processor like this?

If so, it looks to be a standard immersion heater, commonly available in the UK. If you can measure the OD of the thread it should be 65.7mm and check the length of the element. Assuming you have a 220v electrical supply in Greece, a standard heater from the UK will be fine.
Confirm the above, let us know and we can point you at a website from which to buy (unless you are happy to sponsor a mad Welshman on a two week holiday).
With the filter, I suspect the arrangement is to pump "finished" bio direct from the processor to the car. If this is the case, it would be a very strong recommendation to up grade the system and install a settling tank and possibly dry wash tower as a minimum. It will improve the quality of you bio dramatically and be far kinder to your car.