Remove the cap from the tower to expose the shank nut. Leave the faucet on the tower as you can use it for leverage. Hand tighten this nut as tight as you can. This nut is constructed out of brass which is a very soft metal. With this, use either a chisel or flat blade screwdriver and hammer to catch an edge of the shank nut.
Tap with the hammer to tighten. Eventually you will develop a small groove in the nut to prevent slipping. You may require help from your drinking partner so that they can hold the faucet in one position while you tighten the nut in the above manner.
To prevent future issues with the shank, you may want to utilize this
lock washer.