I live in a house from the 60s that somehow never had a back flow valve. My insurance company is pushing me to get a back flow valve installed before they will provide basement flooding insurance.

The house has a single water inlet pipe and a single sewer outflow pipe.

I just had a plumber come to give me a quote for installation and he said that i'd need a back flow valve at each location where I have appliances or drains installed in the basement.

This sounds bogus to me; back flow valves are to prevent sewer water entering through the drain; right? There's only one drain, so only one valve is needed; correct?

Is he taking me for a ride?