Set the strainer over a large bowl so that it won't move when being used. Center a coffee filter in the middle of the strainer.
Stir the mixture of flour and water to remove any sediment that may be at the bottom of the container, using a long-handled spoon. Scrape the bottom of the container and stir all the flour into the water.
Pour the mixture through the coffee filter and strainer very slowly. Keep the liquid inside the strainer and don't allow any to splash out over the edge.The flour will stay inside the filter and the water will drain through to the bowl below.
When the filter gets completely clogged and no more liquid will pass through, remove it and replace it with a clean coffee filter.