Having used a Millbank and seen(and tasted) the clarity of the water coming out, I don't think a handkerchief is going to give quite the same effect. The millbank bag has been designed in a certain way to get the maximum filtration from the materials. When I last saw one used it took about 2 hours to fill a small glass, admitedly that was very dirty water, but doing the same thing with a hanky I suspect would be a little shorter in time and therefore more stuff would get through.
I think I'll stick to the Millbank, but thanks for your ideas!!
Miggers, thanks for the info, thats more the price I'm looking for!!