Open the bonnet and locate the water bottle, down on the left at the bottom of the bottle you will see your pump sitting in it, pull the pump away from the bottle and then tug carefully at the pump until it comes away, no need to disconnect it from the water pipe or electics ( but If you do be very careful not to break the plastic bit that the pipe connects to, its very brittle!!! trust me!!!) pull out the filter, as said it looks like a rubber cromet, now clean it and put some washing up liquid in the filler neck and wash through thoughly with a water hose, may also help if you lift the low water sender unit out as well (between the pump and filler neck, about half way down!) once rinsed replace everything and fill with water and then run until empty!! might have to refill and empty a few time until all the grunge is out!! I had to. When you are happy fill with water and your desired screen wash.
Hope this helps
Rob