bathroom venting question

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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snipped-for-privacy@gmail.com wrote in

I installed a trap similar to an pside down plumbing trap to prevent cold air backflow. The tap went up to hold warm air which prevented cold air from entering. Worked like a charm for 20 years. The trap has to contain warmer air than the outside air temp so it has to be insulated and in the attic as close as possible to the warm air source (bathroom). Sloped the vent pipe towards the outside so condensation would drain outside but never saw any stains on the outside of the house or other evidence of moisture. This is in Winnipeg where winter temps average well below freezing for 6 months.
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