Grate soap into flakes. (I used my KitchenAid grater attachment.)
In a small saucepan, boil 1 cup water.
Pour water into a high speed mixer. Add the soap flakes, vegetable glycerin, and tea tree oil. Cover and pulse until the soap flakes are completely blended. Be aware that this can get very foamy.
When the bubbles have settled, blend or stir in an additional 4 to 5 cups of water. Transfer to an 8 to 10 cup bowl. The soap will appear very watery but will become a thick gel as it sits at room temperature.
When the soap has become a solid, whisk or blend in the remaining water, adjusting until you reach your desired consistency. Divide liquid soap into containers using a funnel.
Over time, the liquid soap will separate. Just shake before using.