First, use PPE
If you get it on your clothes they are fuuuucked.
Wear proper gloves and face protection.
Always put the water in the mixing container first (you don't want this stuff splashing back up on you).
Second
Mix it 5 parts water 1 part hypo and see how you get on.
If nothing much happens after 30 mins then make it SLIGHTLY stronger.
Be aware of plants and grass etc (it will kill them).
As Nathan said, soak them with water first (so they don't soak up the hypo) and then rinse again after.
If your custy has Koi carp, it will kill them.
Third
Test it on your own property first and see how you get on.
NEVER turn up to a custy, having never tried it on your own property first.
PS. It stinks.