We are having a pool put in and one of the trees in the yard is too close to the dig site. I told the pool crew to knock it down with their excavator, but he said they could try to move it . So they transplanted a 20-25 ft elm 6-7 inches in diameter a few days ago. I was not home when it happened so I don't know how much of the root system was taken. I know it is stressed but seems to doing ok at the moment. I have been surface watering thoroughly every day and leaving a hose at the trunk to trickle water 24 hrs.

Does anyone have advice on transplanting a tree of this size? Is there a recommended way to water a newly transplanted tree?

Use Superthive vitamin solution. You can find it on Amazon. Get a Home Depot five gallon bucket and drill 4-6 medium size holes in the bottom. Use another five gallon bucket and mix solution with water per instructions. Place the bucket with holes at the base of the tree and pour the water solution from the other bucket into the other bucket with holes. Wait for the water to drain completely and repeat procedure two more times so you do a total of 15 gallons. I'd do this once every week for six months.

Be very careful watering an elm (ours is a cedar elm that we almost killed overwatering). Ours was planted in Late August in the height of the drought. The soil was like concrete and us watering too frequently created a tub of water around it and almost drown it out. Our landscaper dug a hole about 3 foot from the tree and below the depth of the tree, and trenched that away about 3 feet. This allowed the water to escape and to monitor the moisture the tree was receiving. Ours lost all its leaves and three weeks later, came back very strong. I would say just watch the leaves carefully and if you lose them all, do something immediately.

skip richter & neil sperry have very specific directions on how-to
and many ways to contact them

it may take 1-3 years for a tree to die or show symptoms

my personal advice is all black thumb, not to be shared as more die than survive my planting efforts

Pros: Doing this is winter is way better on the tree.

Cons: That crew probably didn't take enough of a rootball. It should be a substantial amount of dirt for a tree that large, requiring that huge spade heavy tractor.

The only thing you can do now is water appropriately, fertilize, potentially drain, and hope for the best.