Wash Kit?!
This will make your kit smell of civilization and give you a huge scent "profile" that will scare off wildlife - so you will never see the beasties in the wilds.
Leave it dirty, smell of the field and wood, see the wildlife, (and look like an old hand... or tramp!) get closer to nature.
If the kit is so filthy as to be unhygenic, brush off the worst, hose down the kit and scrub it with a stiff brush using an old toothbrush in seams and welts, dry it naturally. If desparate to shift stains try vinegar, in various dilutions and as a last resort pure soap flakes and warm water.
John