Editing Bioactive Vivarium Guide (section)

=== Step 1: "False bottom" drainage layer ===
<gallery style="text-align:center" widths="450" orientation="square" spacing="small" position="center" captionsize="large" hideaddbutton="true" navigation="true" mode="nolines">
File:LECA Ball Drainage Layer.png|'''LECA balls'''
File:Filter foam drainage layer.png|'''Filter foam'''
File:Egg crate drainage layer.png|'''Egg crate'''   
</gallery>
Start by building a "false bottom" drainage layer by adding at least 2" (5 cm) of LECA balls, egg crate, or 30-40 PPI pond filter foam to the bottom of the enclosure. This drainage layer ensures that excess water / moisture runs off from your soil, and prevents it from getting soggy.

The differences between each these materials are minor, and they're all similar in price.
Bonus tip: Add 3-4" (7.5-10 cm) of PVC pipe to provide easy access for a siphon in case you need to drain water out later. Just make sure to cap it so animals don't get stuck!