Slow watering. The pipe goes down to the second bucket. There is a plastic cup placed through a hole in the first bucket and sits on the bottom of the second. The dirt is filled into the first bucket - including the plastic cup. The water can leech into the soil through the cup. There is also a strategically placed hole in the side of the second bucket for "excess"' water to drain out. It's actually kind of clever and seems to be working!

I googled on youtube and there are several similar videos on how to make them. Here's one: https://www.youtube.com/watch?v=EObxoOPhN2E