Line a medium-sized glass bowl with a thin, white floursack cloth (I use these). Carefully pour in the regular yogurt (either raw or pasteurized) in the middle of the cloth.

Tie up the ends of the cloth with a rubber band and attach to the knob or handle of an upper kitchen cabinet with the glass bowl directly underneath.

Another method is to tie a thick knot with the ends and wedge it inside the cabinet door to secure (see video below).

Allow the liquid whey to drip into the bowl for 10-15 minutes. About 1/2 cup of whey will drip into the bowl in that amount of time.

Carefully remove the bag of yogurt from the cabinet door and place into a clean bowl. Unfold the ends and scrape out the Greek yogurt into a clean glass container. 

The leftover liquid whey should be refrigerated in a small glass mason jar with a lid. It will last up to 6 months and is useful as starter for fermented recipes.