Don't do it. All you'll be doing is creating a breeding ground for anaerobic bacteria that have great potential to rot roots. The bacteria will also produce methane, excess CO2, and sulfurous gas compounds that will impair root function and reduce plant vitality. Put your holes on the bottom at the container's lowest point. Containers that need more frequent watering generally offer much greater opportunity for plants to grow as close as possible to their genetic potential.

Al