Joe Out of curiosity, I looked at the Microphor website. Interesting toilets. It looks to me like you don't need to add anything. The toilets include a vacuum break on the flush water valve. That should provide backflow prevention, shouldn't it? This looks similar to the VacuFlush toilets. There is a vacuum break in line with the flush water and located just a few inches above the top of the bowl. They connect directly to the pressure water system without any additional devices. Jim Fidler "Fiddlesticks" ---------------------------------------------------------- According to ABYC I will need to use some kind of backflow preventer system. Will a simple siphon break suffice or do I need to use some other device and if so, what? Joe Engel