+1 on the Hepvo Traps!
I've been using mine for a few years now and it has performed flawlessly. I ran my drain right through the floor because I couldn't afford to loose any height, 6 ft tall interior, 6 ft tall biker. But I didn't want to have a P-Trap hanging down and to interface with the black tank would have been problematic at best. Hepvo solved all those problems plus the added benefit of being a waterless trap means you can't get the sewer gas smell in the trailer, unless your driving through Juarez! Ay Caramba! Traditional traps can also dry out when not being used or even be sucked dry at highway speeds leading to that familiar "Outhouse on Wheels" syndrome.
If the water is not in the trap, it's just a vent for the blacktank, and path of least resistance and all, that's probably where the gas will go and stay. Carpets, drapes, clothes, bedding, dogs, food, furniture are all great collectors of funk. Also, Hepvo won't let liquids or solids backup into the drain from the tank. Nice!
I don't know what you have planned for your plumbing system, but I went with a black tank only. So grey water can also go there or... put in a diverter valve so you have the option to drain grey water ( shower/sink) to the ground when acceptable. That helps to extend the time you can go before needing to empty the black tank. You can always grab a 5 gal can or two for fresh water refill and not have to take the rig to town till you have filled the black tank. I have never come close to filling the black, even 10 days/ 2 people.
You are making lots progress there. Just keep chipping away at it and it will be done before you know it.
Happy and Prosperous New Year to you and yours.
McDave
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