We are considering dual flush toilets rather than low flow. There are 2 kinds: Toto (popular seller) with a smaller flush pipe dia. and standard install or Carona (Australia's favorite) with a 4 inch pipe and a special install and 4(!) 90 degree turns. We have 2 toilets and 2 adults, we live in Portland OR & water prices are going up, up, up. Any thoughts Anyone?