What you call a groomer we just call a drag. I built the airport at Burning Man for a few years, looks like I will do Afikaburn's next year as well. Simple tools are the key to making it all happen. We built our own drag out of 6" 'I' beam steel 4'x4'. Essentially it was two legs, with both ends kicked up and two cross braces. Put some shackles on one end and used 20' of chain to make a 'V' to tow it with. Took us around 4 hours to make it out of the scrap 'I' beam. It works well since it is heavy. It will work on soil with good effect. It will scrape down ruts by dragging the high parts to low if you cross at a 45° or so. If it is hardened dry clay it will not work so well. Rocks, not well at all.
Make lots of passes to even out things. Deep ruts, well... get your shovel to speed it along a bit. If you want your now more or less smooth surface to last, hope for rain or borrow a water truck. You need to stabilize the soil to make it stay put or it will just move or blow around. To put it in perspective, I used 30,000 gallons a pass, 3 passes on each 5,000' runway. Helps if you have a roller of some kind while the soil is moist.
