On Wednesday, December 12, 2018 at 6:14:54 PM UTC+2, Pete wrote:
What filters are you recommending that cost nothing and work well? I was thinking of going to Autozone and buying small-motor gas filters?
If there is something better I would like to use it.

Yes they are small gas filters from auto parts store. Smaller is always better, with big filter you are effectively increasing the tube volume between instrument and probe which can be problem for variometers.