Incorporate the caustic soda and water in a bucket using the ratio 1:2. For example, if you add 1 cup of caustic soda, add 2 cups of room-temperature water.
Attach a 1/4-inch drill bit to an electric or battery-powered drill and drill through the visible portions of the stump. Space drill holes about 3 inches apart.
Stir the caustic soda solution, then immediately pour it all over the visible stump and down into the drilled holes.
Reapply the caustic soda mixture once every week for approximately three to four weeks. The caustic soda will spread into the root system and kill the tree's roots. The stump itself will also become weak. When the stump is soft enough to break apart with your hands, use a shovel to dig up and remove the stump. The roots of the tree will decompose in the ground.