If you are building one, you will have to chose where to place the drain hole. If the plant will be watered once a day, it should have about one quart of water in the water reservoir. You can pour a quart of water into the bucket, draw a line, empty the water and then put a drain at that point. Where to place a Drain Hole To create a hydroponic grower out of the tub you cut a drain hole on a side. The drain hole can be placed anywhere along the side, and where it is placed will determine the water table in your grower.
Plants grow with their roots going towards the water table.
The plants vary in how much area they want in the ground before they find a water table and so where you put the hole in the side of the tub will determine which type of plants will grow best in the tub. Deciding where to place the drain hole determines what kind of food you can grow in the tub. There is a hole template in the kit to help guide you in drawing the hole. It should be placed so one lip of the grommet is tight against one side of the bucket and the other side is tight against the other. The grommet should keep the bucket water tight once the pipe is placed in the grommet.