Its really good for getting out stains. Just be careful. If it does not say for coloured then DON'T use it for anything except whites or dish clothes as it will take the colour out.
When the girls were small I used to soak all the nappies (white) in it then put the nappies in to wash. It didn't seem to upset their skin as it was removed with the wash then rinse cycle.
I still used it to remove stubborn stains, especially good on cricket whites, but I use the one that's safe for coloured clothes.
For a nappy bucket size, you use about 3/4 cup and then dissolve it in water. Soak it overnight then wash. You can tip the solution in the machine when you start the washing as when you fill the machine it dilutes.