Put one of these Siphon vents in:
Believe me, I was skeptical of these things, but they really work. I have absolutely zero stink problems.
They are designed so that they develop low pressure as wind goes across them. The stronger the wind, the lower the pressure. The low pressure sucks the air out of the holding tank as you drive down the road.
Otherwise, as you drive down the road, air pressure will be reverse and push air into the vent, which will cause stink inside.
These improved vents are being OEM'ed for many of the better brands of RVs. But they cost $35 or so, vs $0.99 for the cheap vents Thor uses.
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