On the Valiant, for some reason, we had to practise chucking this stuff out, I seem to recall, once every six months.
The main circuit breakers for the Window Dispensers were actually in the bomb bay rather than the cabin. I recall being 'checked' by somebody on the Windows sortie and I'd forgotten to check the CBs in the bomb bay prior to taking off, so he was able to point out my incompetence (I was a very green 20 yr old)to the Flt Cdr.
Actually, on the sorties we flew over the Kola peninsular in the northern USSR it was all we had in regard to counter measures apart from the utterly useless Orange Putter, and, c52000 ft altitude.
Incidentally, to check the Orange Putter was working we fired a Very cartridge full of window and it showed up on the screen as it dispersed.