In a medium saucepan, mix together the shredded Fels Naptha soap with 4 cups of water. Heat on medium/high, stirring occasionally, until melted. Fill up a 5 gallon bucket halfway with hot water. Pour in the melted soap/water mixture. Stir. Then stir in 1 cup of borax & 1 cup of washing soda. Stir in the essential oil, if using. Add more hot water, filling up the bucket a little more than 3/4 of the way full. Put the lid on it, and let it sit for 24 hours. Then, stir in the bottle of Tide. Add 1/2 cup for regular large loads.