I think I have solved the dust and drying mark issue on my film. After several searches online I decided to do my final wash in de-ionised water. I also added a drop of LFN wetting agent and a capful of 99% isopropyl alcohol – which is supposed to enable the water to drain off the negatives much more smoothly and dry at a faster rate.
However, the first time I did this, although it improved matters, I was still getting some drying marks on the negatives.
So in the end I resorted to the squeegee method. Many people advise against this as squeegeeing the film can leave scratches on the negatives if there is any grit or dirt on the squeegee. I rinse the squeegee in the final wash water before using it and it seems to have solved my drying mark problem.