Black water tank blowup

[bertschb]

Wow. I wonder if that’s my issue; leaking seam? 351m, 6 months old. Didn’t overflow it but my interior smells like sewer while In storage in my shop building. The smell is strongest underneath bathroom sink where the cut through hole is for all the pipes. Weird is that it doesn’t hardly smell in the basement storage area. Already have appointment for drop off at dealer next week.

You may want to check if you have an AAV valve under your bathroom sink. Pretty common for them to stop working which results in stink under your sink.

[Wicked ace]

You may want to check if you have an AAV valve under your bathroom sink. Pretty common for them to stop working which results in stink under your sink.

On a previous TT I found the AAV just wasn't screwed in tight, only a thread or two was caught. Once tight the smell stopped.

[geotex1]

Wow. I wonder if that’s my issue; leaking seam? 351m, 6 months old. Didn’t overflow it but my interior smells like sewer while In storage in my shop building. The smell is strongest underneath bathroom sink where the cut through hole is for all the pipes. Weird is that it doesn’t hardly smell in the basement storage area. Already have appointment for drop off at dealer next week.

That is likely your grey tanks. Look under the sinks and you will see economy version automatic drain vents/air admittance valve. Replace with higher end Sure Vents and disinfect your grey tanks. They get quite nasty depending upon what is in the water and what you put down the galley drain - ever see what grows out of scratch pancake batter? Toss the rest of a beer down on it too... Good ole lemon PineSol works great, or you can buy the more expensive task-specific stuff from your favorite RV supply.

[boyscout]

If I may make two suggestions in the interest of health and safety. I realize there is an internal check valve at the water connection but adding a second after (downstream of) the ball valve. Better yet a back-flow preventer.
https://www.amazon.com/Camco-23303-B.../dp/B000EDUTN6
The second is to at least spray paint that white water hose to identify it as black water use only. You really don't want those mixed up. I use a green garden hose as needed.

Excellent points. In my particular instance, however, I use blue FW hoses for my potable water and only own the single white hose so I'll never confuse the two. Definitely something to think about though!

@Running on MT if you are interested in health and safety then DO NOT put a backflow preventer on your black flush inlet! Really bad idea.

Some of the most plumbing-knowledgeable GD owners around including @Cate&Rob have made a good case against doing it, and against leaving the black flush water supply connected to the inlet. Here it is.

The black flush water supply rises from the hose inlet through a plumbing line to high up inside your trailer, probably up behind your shower wall. It connects there, feet above the black tank, to a valve that creates a vacuum break. From there it continues back down from the valve and into your black tank.

When you send pressurized water into the black tank flush inlet it creates a feet-long column of fresh water up to the high-up valve before it continues flowing down into the black flush mechanism in the tank. That column of fresh water is a deliberately-designed buffer between the inlet and any bacteria-laden water in the tank and black flush mechanism.

Each time when you finish flushing the tank you should remove the black flush supply hose and allow that column of fresh water to flow out. The feet of fresh water on the inlet side of the valve flows back out the inlet and the feet of mostly-fresh water on the other side of the valve flows down into the tank, carrying any bacteria on that side of the system with it.

Trapping that water in the system - by installing a backflow preventer or by leaving a hose full of water attached - defeats the purpose of the vacuum break safety system. It leaves a column of water - a pathway for pathogens - all the way from the tank to the inlet (and into your hose if left attached).

On the other hand, allowing the fresh water to flow back out of the system drains the pathway from both the up and down sides of the vacuum break system. You can then reattach the black flush hose if you want to.

However, to be thorough, the second part of Wicked ace's advice is made unnecessary by your new understanding of how this system works. You can use the SAME HOSE for black flush and the trailer's city water supply! As long as you disconnect from black flush immediately after you turn off the water to it, you can simply move the hose to city water and turn it back on again. Nothing but fresh water has passed through the black flush inlet. However if you trap water in there, that's when it can get risky.

The system works like this for a reason: health and safety. You likely know that Grand Design doesn't generously load up our trailers with unnecessary things, especially things hidden inside walls like the black flush vacuum break system that most people don't understand. It's there for a reason.

[Running on MT]

remove the black flush supply hose and allow that column of fresh water to flow out. The feet of fresh water on the inlet side of the valve flows back out the inlet

Everything you said somewhat makes sense on its surface, but I have owned two rigs with black tank flushes and only recently installed a valve on the inlet. In the hundreds of times I have flushed my tanks without a valve, I have never seen any water flowing back OUT of the flush inlet.

Anyone else have any thoughts on this?

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[vonzoog]

Thanks boyscout for the post.

The post makes absolutely perfect sense to me. I have always wonder why there is a small flow of fresh water out of the connection when disconnecting the water hose. I never understood why anyone would want to leave a hose connected to the black tank connector.

Thanks again.

[boyscout]

Everything you said somewhat makes sense on its surface, but I have owned two rigs with black tank flushes and only recently installed a valve on the inlet. In the hundreds of times I have flushed my tanks without a valve, I have never seen any water flowing back OUT of the flush inlet. Anyone else have any thoughts on this?

I've owned two Grand Design trailers - 2018 Reflection, 2018 Solitude - and they both worked like this, including the flow out of the inlet when the black flush supply is removed.

The guy who schooled ME on this owns a 2015 Reflection. If you search here for posts by @Cate&Rob you'll find him discussing this and others supporting his advice.

[Running on MT]

I've owned two Grand Design trailers - 2018 Reflection, 2018 Solitude - and they both worked like this, including the flow out of the inlet when the black flush supply is removed.

The guy who schooled ME on this owns a 2015 Reflection. If you search here for posts by @Cate&Rob you'll find him discussing this and others supporting his advice.

Perhaps I just haven't noticed. I'm going to disconnect the hose the next time I flush and see what happens!

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[Cate&Rob]

Everything you said somewhat makes sense on its surface, but I have owned two rigs with black tank flushes and only recently installed a valve on the inlet. In the hundreds of times I have flushed my tanks without a valve, I have never seen any water flowing back OUT of the flush inlet.

Anyone else have any thoughts on this?

There is a column of water from the vacuum break to the inlet connection, and a similar column of water to the tank, which are both released when the water pressure is removed and the vacuum break opens. The only way that you could not have seen this water coming back out the inlet is if you leave the hose connected when you shut off the pressure and this water actually comes out at the vacuum break device at the post faucet. Most campgrounds have this faucet vacuum break . . . some do not. As @boyscout has described, leaving a hose attached to the black tank flush is just asking for trouble.

As I have described in the past, I see many campers with two separate hoses attached. One to the fresh water inlet and one to the black tank flush. These are T'd together at the faucet as if distance from the camper is some sort of safety. Then, they dutifully turn off the post faucet when they leave the camper. Now . . . the black tank flush line is directly connected to the fresh water inlet.

Never leave a hose connected to the black tank flush unless you are actively flushing the black tank! There is no risk to using the same hose, as long as it is either flushing the black tank or pressurizing the fresh water system. Never both. This is how the system is designed to operate.

Rob

[SGT ROC]

Everything you said somewhat makes sense on its surface, but I have owned two rigs with black tank flushes and only recently installed a valve on the inlet. In the hundreds of times I have flushed my tanks without a valve, I have never seen any water flowing back OUT of the flush inlet.

Anyone else have any thoughts on this?

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My current rig is the only one I have owned with the black tank flush. I do see water flow back out every time I finish flushing and disconnect the hose. And I never leave the flush hose connected. I have heard one to many horror stories about the potential consequences of that!