We will now layer materials in the tub.
First, hop in your home-built electric car
, and drive to the local landscaping supply store. Get yourself some big stones, little stones/pebbles, sand, dirt (if you don't already have some,) and landscaping fabric.
In my case, the cheapest bulk way I could buy materials was by the 5-gallon bucket, so I brought a few with me.
Layer up materials in the bottom of the sink in the following order.
1) Big stones over the drain (to keep other smaller things from getting in there and clogging it up.
Then add a small piece of landscaping fabric over that, pinned-down by a few stones.
2) A layer of the big stones. One or two stones deep is fine. This is for good drainage.
3) A layer of pebbles. (It should make a more or less solid layer. The pebbles should be big enough to not fall through the spaces between the bigger rocks.)
The landscaping fabric. (My piece was about 3' by 4'. Fold the edges like a Chinese take-out container)
4) A layer of sand, about 2" thick
5) A layer of dirt, about 2" thick
The landscaping fabric is there to prevent the sand from working its way down into the drain. Since the fabric is floppy, you will have to hold it back out of the way while you add the sand and dirt. If you have 2" spring clamps around, those work well to pin the fabric back too.