I suspect paraffin might be more effectrive as it's more penetrating than water. Is there an oil you can treat the hens with? It kills mites by blocking the spiracles and suffocating them.
Unlike varroa mites, which spend most of their lifecycle on the larva or the bee itself, red mites don't spend time on the chicken except to suck their blood.
Most of the lifecycle is spent in crevices in the housing, especially the roof and the ends of the roosting bars.
But just like varroa, you have to disrupt the entire lifecycle for the treatment to be effective, otherwise eggs will survive to breed a new generation of mites. In a poultry house you have to keep repeating the treatment, which is a nuisance and is expensive.
The tradtional way to treat red mite was to paint the inside of the house with creosote. Creosote is now only available to professional users, but creosote substitute works fairly well. The big disadvantage is that the house becomes uninhabitable for the chickens for about three weeks until the creosote has dried and the house has been well ventilated. So you need a spare house during treatment.
Modern plastic housing is best for red mite control, since it can be regularly pressure washed and both mites and eggs blasted away.
