I fill the two holes with moist packed potting mix, That becomes the wick system for the container, Then the rest of the bin is filled with potting mix so the depth of the container becomes 10" or so and the roots actually will seek the water reservoir thru the smaller holes.
The bottom is actually the lid for the container, I trim it to fit inside the container, Use mainly 18 gal Rubbermaid roughnecks, They last 4-5 yrs or so before the sun drys them out.