I have had exactly the same problem , and my solution is not perfect so I am looking for a better way too. The former owner of my house was never smart enough to install a floor drain in the double wide garage and worse the floor slopes toward back wall instead of out overhead door. My first idea was to just cut a hole in floor and let the melt water from the tractor(with chains) and ATV run on floor and then squeege it toward hole, but I was warned by a friend that an major amount of water sitting in the gravel under the garage floor could freeze and crack the floor close to the outside wall where frost could penetrate by midwinter (its minus 20 farenheit today here), I have lots of clay around here so the 4 inches of gravel under floor won't further drain very much. I keep garage heated because it is my workshop. So this winter I put pressure treated 2x 4's ramset to floor then I caulked the 2 x 4 with mono caulk so that water gets directed to back wall where it eventually ends up anyway. At the back wall I chisled out a bowl of concrete roughly 12 inch diameter 3 inches deep so not right thru the floor ) Now I just wet vaccum up the depression in concrete. But it only holds maybe a quarter the amount of a typical snow melt (yes still brush off tractor before bringing in)
So my next step might be to chisel the bowl right thru the floor and cement ? a pipe from the outside of back garage wall and run it a few feet out from the foundation to drain outside . The inside depresssion is only 12 inches inside the back wall so might be able to do it all from outside.........but still leary about winter freeze up of water. All this to say your not alone, AND ANYONE BUILDING A GARAGE PUT A FLOOR DRAIN SYSTEM IN IT !!!
