I frequently use cheap supermarket Cola in my waste tank. It certainly kills the smells. How it would react in pipes is probably ok, but if there are metal fittings in the system it might be more of an issue when you see what it does to coins. I seem to recall it contains phosphoric and citric acids (albeit probably very dilute). Puriclean (powder or tablet) seems to be formulated specifically for the task of sterilising pipe work and fresh tanks.
I use cheap Lidl or Aldi cola about 40 p a large bottle,put 4 bottles down the plug drains inc shower,drive around for a bit then dump it out
works and cheaper than elsan drain clean
another tip is scrape plates etc clear before washing in the sink as it stops all crap getting down and into waste tank which also helps reduce odour in very hot weather etc