2 parts clean wood ashes, 4 parts local dry dirt or fine sand, 1 part amorphous diatomaceous earth, to be completed at their leisure. Bathing in water? Wait for a good rain. You might perform an Advanced Search on something like `bathing show birds' , I know some members DO toss Silkies `in the tub', but anything more than hoping an adult turk gets in range of the sprayer on the hose, here, would be far too stressful for all involved.