The best way to purge dust is to include the dust addresses in with your normal use wallet.  I've had plenty of dust go to my mainly used address, some as small as 3 satoshis, but they've all been spent at one time or another with larger BTC outputs, automatically.  At one time, I looked at the unspent transactions, and had a dozen or two, but now, I only have 3 unspent outputs.  And I've never paid more than a 0.0005 BTC fee, either.