Nicky,
I going with the assumption that your tires are steel corded, if so this is what Jay did:
tire is laying down, score the tire with a chain saw, (not into the steel cords)drill a hole into the tire big enough to start a Sawsall blade,(he used a Milwaukee blade, (the most aggressive you can, can't remember exact name) cut away with the Sawsall, he can do one in 15 to 20 minutes. Installation : We dig ours down in the ground enough so calves can drink too, fill the center full of cement, we use a Johnson float with a bleeder valve, use a 4 inch PVC pipe for draining and dig a 20 ft drain field with a 55 gallon drum with holes in at the end thats buried roughly 6 feet down. In the center he makes a cage around the float and drain out of hog panels
Hope that helps, I can take some pictures if you like tomorrow