We used this bath to mix our clay when filling the workshop walls in with wattle and daub.
It has been empty for almost a year and I finally decided where to put it. It is a large volume to fill and I was looking for a very free draining medium to plant thyme into.
So after filling the bottom with stone and broken pots I put in a thick layer of birch sticks which were cut down 2 or 3 years ago and topped this with a mix of soil, compost and grit.