"Rod" wrote in message
...

In the greenhouse of somewhere I lived in there was a slate water tank.
IIRC (and it was a long time ago) the slate was very smooth and dead
square - I'd guess around 25mm thick. The two end slabs had channels cut
into them - that just like you might do with a router for a piece of
wooden furniture. The other sides slotted in. I have a feeling that the
base might have had some similar machining.

Wish I could remember more detail - there simply must have been some sort
of tie rod but I don't remember seeing one when the tank was in place.
Maybe holes were drilled through the slate from one end to the other?

It may have been glued..
aquariums are only glued together these days.
It may have had dovetail slots to help keep it together while the glue set.