strong detergents accumulate in the soil....and stop water from penetrating into the loam structure, they also kill nitrogen fixing bacteria, and other useful bugs..and cause worms to come to the surface where they are heavily predated.. maybe you gould use your grey water 'one time in three' to minimise the effect.. just a thought though a bar of simple soap will jast a lot longer than a bottle of shower or bath bubbles
Shampoo should be ok as you would use so little and the dilution would be pretty weak