Before and after 3rd try

One last try yielded about the same results as the first try.  Here's the yellow looking result, which I think is indicative of a lot of charcoal not getting filtered out.

One last pour and the napkin below it.  This last pour is with a napkin over a plastic cup.  It may have helped a little, but I lost a lot of water trying to get it into the glass.  That's why the water level is lower.

This is all I have time for right now.  Something of a disappointment, but we'll get 'em next time.  ( famous last words )

Update:

Analysis after cleanup:

There's a problem maintaining the integrity of the layers.  The sand wants to run all the way down to the cotton layer, which is the last layer.  This does two things  1) it reduces the  effectiveness of the sand layer and the cotton layer and 2) it clogs up the cotton layer which reduces throughput.

The breakdown appears to be around the edges or the perimeter of the plastic container.  The container is very flexible, so when I pick it up, it flexes.  I think the flexing is what is destroying the integrity of the layers.

I could swear also that this isn't 100% sand.  It may have some clay in it, too.  It shouldn't clump together the way it does.

Thoughts to chew on.