When we bought our 84 westy, the sink's water pump didn't work. So we 
opened up the tank and boy did it smell! The pump, it turned out, had 
burned a hole in itself. 

It is a blue cylindrical thing. Any idea how much it costs and if an 
after-market RV-type pump would work? Also, do these pumps leave any kind 
of toxic residue in the tank when they self-destruct? I've poured boiling 
water with lots of baking soda in the tank and rinsed it so that it 
doesn't smell anymore. Should I also use chlorine?

Any help is appreciated.