What do you do with leftover bits of soap??? I usually throw them away but I was given a good idea from a friend of mine. Take those left over bits of soap and place them in a large jar and fill up with hot water. Leave this soap soak for a couple of weeks and then stir regularly to dissolve. You can even chop or grate the soap before adding to the water. When dissolved (after a couple of weeks) use this liquid in your washing machine.
My friend uses it on their work clothes. Once you have used most of it top it up again with hot water and add more soap as it comes along.
PS: one thing to watch if using on good clothes is that you don’t get bits of soap that hasn’t dissolved on your clothes. You may want to pour it through a fine sieve into your washing machine.