The small pipe fits down in the seed cup and doesn't spill out to the sides so you can plant down to the last seed and not have to scratch it down to the feeds. I also marked the inside of the large pipe every 1 inch to help me keep track of any feeds not planting alike. Wish I could take credit for the idea but my brother came up with it several years ago. You are only limited on diameter of the large pipe by the opening of your drill box lid and availabilty of end caps. I try to get 3.5 to 4 lbs. seed per acre but with a drill it is as has been said a controlled spill. Pictured is 6 inch PVC used in a different drill.