I have no idea who gave you this erroneous information about combination systems.
I am not only licensed to install these devices according to code but I also am consultant to several engineering and law firms in NYC.
I just financed a chemist for water quality testing to work with my plumbing company so we now can offer water quality testing plus the labor and expertise to install the filtration system required.
By having Richard as a major team player we now have the credibility of have another professional as part of the team with all testing performed in my new offices
My normal fee is $225 per HR (minimum of 4 hours consultation) BUT if your planning on doing a lot of this type of installations I am sure we can work out some type of agreement where we both make money.
Considering even a 4″ back water valve can NET over $1,200 you can realize a profit from the get go.
I have installed lots of these back flow valves with certain restrictions which you must be aware of.
Please feel “free” to contact me privately and we can work out any of the finer details you may need answers to.