If you use solid soap, over time it leaves behind scum — small pieces.
Of course, you can throw them away, but you can give them a second life by creating liquid soap. It's simple, environmentally friendly, and economical.
Gazeta.ua shares two ways to create new soap from leftover soap — liquid and solid bars.

How to create liquid soap
What is needed:
Collect the soap residue in a jar until you have accumulated approximately 100 g.
Prepare a bottle with a dispenser (300–500 ml).
Grater for rubbing soap.
Ingredients:
100 g of soap residue (grated).
500 ml of hot water.
1 tsp lemon juice (or juice of half a small lemon).
1 tbsp. l. glycerin (about 2 caps).
How to cook
Grate the soap residue on a fine grater to speed up dissolution.
Pour 500 ml of hot water into a dispenser bottle or separate container. Add the grated soap and mix thoroughly to dissolve the soap.
Add 1 tablespoon of glycerin and 1 teaspoon of lemon juice. Mix well again.
Let the mixture steep for 2-3 days, shaking occasionally to ensure all ingredients are evenly mixed.
Before use, pour the finished mixture into a dispenser bottle (if prepared in a different container). Always shake before use.
You will get a wonderful liquid soap with a pleasant aroma, which is perfect for hands and even for delicate washing.
How to create solid soap
Collect a certain amount of soap (it would be interesting if they were different colors), grate them. Place them in the microwave for 2-3 minutes. Grease a plastic soap dish with oil and pour what you took out of the microwave into it. It will be a creamy mass. Smooth it out with a spoon, and in a few hours you will have a new multi-colored piece of soap.
You can also make a soap scrub.
Add ground coffee, oatmeal or sea salt to the melted soap. Mix, pour into a mold and let set.