Does anyone know anything about Thermostatic Mixing Valves, and whether
one would be suitable for an outside tap to provide warm water to wash
the dog with? I'm thinking I'd connect the hot & cold feeds to the TMV
(inside the house), then set the temp accordingly and chuck a tap on the
end (outside the house).

I've seen some TMVs on ebay for under £25 which sounds reasonable.

Thanks,
Ant