napisan or similar to soak stained clothes?

i use disposable nappies, but when i came out of hospital my mum bought me a tub of bio something, similar to napisan for soaking reusables - so that i could soak lo's stained clothes before they went in the wash. ive only just run out and can't find it or any similar product anywhere. any ideas where i can find some? Have just bought a tub on amazon but there was only one left and am paying postage - so next time would love to know where i can pick some up x