That "vent" under the sink is a vacuum breaker. There is normally one under the galley sink also. It allows air into the tank when you dump the tanks so the water won't be sucked out of the traps as someone else mentioned. If it is stuck shut, the water can be sucked out of the traps, and you will get odor. If it is not closing properly you will get odor. It is easy to unscrew it and take a look at it. Some have a simple rubber flap setup, and some have a spring mechanism.
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Paul (KE5LXU) ...was fulltimin', now parttimin'
'03 Winnebago UA 40e TRADED OFF JUL 2023 / '17 Jeep Grand Cherokee toad
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