Originally I saw this method on a You Tube video.
I tried their method and it worked fair. I didn't like how it was twisting my "Well Screen Pipe". I completely pulled the first pipe back out of the ground, rebuilt the drill head. Started by cutting teeth on the bottom pipe. Then glued the funnel shaped piece inside the 4" pipe. That piece is actually not made for what I did with it. It's a 3" x 2" threaded adapter. I ground the outside tabs off so it would fit inside the 4" pipe. I then installed a 2" PVC pipe down the center of the main 4" pipe. Screwed (has a male threaded end) it into the funnel shaped adapter I had previously glued inside the toothed pipe. This stopped the 4" piece from back filling and getting clogged. It also gave me more water volume at the bottom, since I wasn't filling a 4" pipe. It also increased the water pressure. It actually cut faster and a lot easier.. When I got to 27 ft.I stopped drilling, and I just unscrewed the center 2" pipe and removed it from the inside of the 4" pipe,
I learned it takes one garden hose to go the first 10 ft. length of pipe. Then you have to add another garden hose for each 10 ft. you go down. On the last section of pipe, I had three garden hoses and my air compressor hooked to the drill head. I should add, each garden hose has 80 lbs. of pressure. A person might be able to do the same with a high pressure pump. The water is needed to wash the drillings up to the top on the outside of the pipe.
I was amazed how the toothed PVC cut thru tree roots over 1" in diameter. That is a huge Sugar Maple tree, maybe 80 ft. tall.
First pipe goes real easy. Just keep rounding out the drill hole to be larger than the 4" pipe.
Second section takes a little more work.
The last section took 3 garden hoses and an air hose to wash all the drillings to the top. Be patient and it works fine.
Then with a little luck you get to this point.
The first pipe to go down was a 10 ft. piece of " Well Screen". It has slots around the pipe to allow more water into the pipe. The You Tube method just didn't work for this type of pipe.
Oh, the guy up in the tree, I help him and his wife each fill their cow elk tags a couple years ago. Helped the guy in the white T shirt get his elk also.