How can I fix my Indesit WD10 washing machine?

My indesit WD10 washing machine does not always fully empty and I suspect that possibly the filter has become blocked over the years.

I have tried to remove the filter, however the cover turns to the left about half a turn and then sticks - I have tried to pull it and turn it a bit more, but am unsure whethere this screws off completely or if it is sipposed to turn half a turn and then pull out.

Can you advise as to what to do as if I make the wong choice I could end up breakinbg it

Thanks

Les