Gregory,

They use to make special cone shaped strainers with a very fine screen
just for this purpose. They are marketed to make "yogurt cheese", sort
of a like a cream cheese from yogurt. I don't know if they're still
made.

You can also just line a strainer with a coffee filter or cheese cloth
or muslin. Do a search for yogurt cheese and you'll find plenty of
info.

Hope this helps,

Ken