Bathroom exhaust fan Q

I have a Panasonic bathroom fan, about 75 CFM. I want to put a backdraft damper at the end of the exhaust pipe to reduce cold air coming in the bathroom. It is one of those spring loaded jobs and says only needs .04 in W.G. pressure to open. I was going to put at the end of pipe to the sophet for ease of installation, rather than inline. Comments, or suggestions? I was also considering a eave vent with dampers by deflecto white plastic, dual side dampers flush mount to sophet. Anyone use one?
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Do you mean .04 PSI? Is W.G. = Waveguide? Is sophet = soffit? What is deflecto?
If you're using a waveguide pressure relief valve, its meant for a dry air system. Such a valve runs offline, not inline with the waveguide, a burp valve if you will. Such dry air isn't coming from bathroom vent. Dave
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