about substrate, temperature, burrow and urine/poop absorb

[Alter-Echo]

I use about 2in of the stuff in most of my cages just for the extra humidity I require and to add some extra absorbing power, but you could probably get away with using a 1in layer since you are using a tub and it will likely be more humid in there. It does absorb urine fairly well, but with a thinner layer you will need to chance it out more often.