Most homebrew shops sell a funnel that has a inset at the bottom to
accomodate a very fine gold filter insert. You can get various the
filters in various grades of filter-a-bility. The filter is about 1.5"
in diameter. This is a very useful tool for filtering must to take a
S.G. reading. It should be about $10 for the whole setup I think.

HTH,
Joe