Buckets often get stuck together so tightly that they cannot be removed using pliers. They can, however, be pried apart using force or hot water.
Turn the buckets upside down
Turn the stuck buckets upside down so the open end is facing the ground. Set them on the ground.
Put your foot through a bucket handle
Put your foot through the opening of the bucket handle closest to the ground.
Pull the top bucket up by the rim
Grasp the bucket closest to you by the rim. Pull upwards, keeping your foot through the handle of the bottom bucket until the top bucket releases.
Run hot water over the buckets
If the buckets are still stuck together, run hot water over the outermost stuck bucket for 30 to 60 seconds. Repeat the first three steps to pry the buckets apart.