I had one of these and watering them was a challenge since the pots that fit into this thing has no holes in the bottom of them.
So fist drill holes into the bottom of the pots.
Second cut the bottom off of a 5 gallon bucket, then get some tubing and since it was on the kitchen counter i just made a tube raining it into the sink.
Now take a bottom of a plastic jar or a lid something that can fit on the bottom of the pot. Then cut 4 pieces that will drain the water from the top pot and drain into the bottom 4. Then the water drains form that into the bottom tray made from the bucket into the sink.