Good shout about the filter, when I took it out a big trail of snot come out with it! Works a treat now...Something I found on another forum on how to do it below if helpful for others...Only thing I would add is its easier to put the filter back in first rather than attaching filter to the pump and then putting back in, because the filter just keeps bulging out when I tried it that way..
"No need to take the bumper off, you can access it from the near side (passenger side) under the car. You don't need to take the plastic wheel arch liners off, but it may help to bend them back a bit if you can, to give you a bit more room.
If you haven't lowered your car, aren't a fat bugger and don't mind working in small spaces, you may not even need to jack the car up like me!
Basically just slide under the passenger side of the bonnet. The filter is on the bottom of the windscreen washer bottle which you should be able to see from underneath the vehicle. You will need to lift the pump up and out of the hole at the bottom of the windscreen washer bottle, when you do this water and screen wash will piss out of the hole, so try not to get it in your eyes and wear some old clothes.
The filter should be black and it may either be stuck on the end of the windscreen washer pump which you lifted up. Or it may still be stuck in the hole of the windscreen washer bottle and you will need to pull it out.
Give it a good clean under a tap with an old toothbrush and blow on it to make sure it's clear, then refit and push the pump back on and top up with water and screen wash 50/50.
Don't think you can refit the pump without the filter to save time in the future. The filter will stop your washer jets getting blocked and also is needed to create a watertight seal with the pump and hold the water in your screenwash bottle.
Nice easy job, should take no longer than 30-45 mins."