Over Generous with the Poultry Shield

Give it a good hose out with just water. That should do the trick.

Once it's dried it won't matter in the least what the original dilution was.  All the water and volitiles will have evapourated so the only Poultry Shield residues which remain will be effectively the same whether you denched it twice with 10% or once with 20%.  Whichever it won't harm your chickens once dry.

Regards