What is the right size and best way to set up a tub?

[Spaniard]

Sure, they can live in it, but are they happy in those things? I know, I know, "Yes! Yes!" you scream.

I've yet to find a snake I can communicate with well enough to know if its truly happy.

Until I do I will stick to other logical indicators that a snake is content for example, feeding consistently, elimination of wastes, breeding and a healthy immune system.

What is it that you take into consideration to deem tub enclosures so inadequate for a bp?