I've been doing what Pete suggested for 2 years now with my  91 westy and
no ill results. 1/4 cup of bleech fill the tank, dirve/slosh around for 10
mins, drain, fush twice with fresh water and away you go..its clean! . I
also flush the sink lines while Im at it. I follow this proceedure twice a
year and no one has died yet ..that I know of.