This is the semi-unique step. Instead of the box top (clever), another bin (pretty good, but expensive), I used some weed barrier I had in the garage. It is supposed to keep weeds down but allows water through. If I needed to buy it, it was about $15 for 100 feet, according to the tag I found on it. Cut to about twice the size of the bottom of the bin. Place in bin, fold corners and put some dirt on to hold it into place. MAKE SURE YOU READ THE NEXT STEP before actually doing this, as these two steps go together.