I keep a container of washed sandbox sand in each female egglaying chameleon's cage from the time the female is 5 months old on so that there is some place to dig to show that she is going to lay eggs.....its better to be safe than sorry. If you don't have the container there and miss the sometimes subtle signs that she needs to lay eggs if can lead to egg binding.
I don't know what size the container is that you are referring to...but the container should be big enough for her to fit into with a couple of inches to spare on all sides and above her when its empty. I fill it about 2/3 full of the sand. BTW...you don't have to wash the sand....the sand would come pre-washed, if you are buying the right kind. I buy one produced by Kings...it comes in a white bag with red, yellow and blue sandbox toys on the front of it. This sand has proven to pass through the chameleon when ingested without causing impaction. It has never caused an infection in the chameleon from any abrasions, etc. resulting from digging like some of the other "sands" that I have used have.
I don't bother keeping the sand moist until the female has started to dig in it. If the sand is level in the container, when she starts digging, you will see the signs.
Some females will actually lay their eggs in this container...others need to be moved to a bigger container. I use a 65 liter rubbermaid container that is modified for the purpose.
I have done it this way for many years.