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Old 09-22-2018, 01:46 PM   #1
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Black Tank Flush System Issue

On a recent trip we were smelling black tank odor. Since I had not flushed the tank yet on the trip, I decided to do so. After connecting up to the dump station, I turned water on to the flush connection and walked to the other side of the coach to check the dump hose. As I stood on the other side, water suddenly began pouring from the area under the slide.
I quickly turned off the flush line and went inside to see what was going on. The interior plastic fitting that connects the water inlet to the coach plumbing had broken off, so water had been just shooting directly into the cabinet under the sink, then ran across the floor and out the other side.
The inlet connects via a barbed fitting to a flexible line which in turn connects to the atmospheric vacuum breaker/check valve. The breaker/valve had not been secured in any way under the cabinet, so any movement of the vehicle or shifting of contents in the cabinet caused stress on and eventual failure of the fitting.
After returning home, I used some pipe strap to secure the breaker/valve unit to the sink base supports. I then fixed the inlet with some plumbing parts I had on hand. The parts I used were not the same as factory, but it is fixed better than factory now. Also, there are attachment points on the plumbing lines to secure them, but this was not done at the factory so I used screws to hold things in place.
I have not had it back on the road yet, but this was likely the cause of my odor issue. BTW, I experienced no ill effects from the "flood" on the floor.
I have attached a diagram of the system for reference
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Old 09-22-2018, 02:08 PM   #2
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So I started to wondering: how many people forget to winterize that connection?
It's an easy thing to miss.
A little compressed air is all you need to avoid a major problem.
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Old 09-22-2018, 02:34 PM   #3
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Originally Posted by barnbnb View Post
So I started to wondering: how many people forget to winterize that connection?
It's an easy thing to miss.
A little compressed air is all you need to avoid a major problem.
Depending on which type nozzle and location on black tank for air only to work! Most use Anti-Freeze pumped in from the Outside shower,that covers 2 things at 1 time! Youroo! !
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Old 09-22-2018, 06:46 PM   #4
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Depending on which type nozzle and location on black tank for air only to work! Most use Anti-Freeze pumped in from the Outside shower,that covers 2 things at 1 time! Youroo! !
You can't "pump in" antifreeze into the black flush inlet, at least on the Forester 2401 WS. The black tank flush accepts only a standard garden hose fitting. There is no outside shower on my unit, or others like it. Unless you fill a garden hose with antifreeze and force it into the flush valve with water or air, you won't have it properly winterized. IMHO, it is best to just blow it out.
To do it right, you need to get an adapter that screws into the garden hose fitting and has an air nipple on the other end. REMEMBER to open the black tank drain valve when doing this, otherwise you may damage the system!!!
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Old 09-22-2018, 08:37 PM   #5
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You can't "pump in" antifreeze into the black flush inlet, at least on the Forester 2401 WS. The black tank flush accepts only a standard garden hose fitting. There is no outside shower on my unit, or others like it. Unless you fill a garden hose with antifreeze and force it into the flush valve with water or air, you won't have it properly winterized. IMHO, it is best to just blow it out.
To do it right, you need to get an adapter that screws into the garden hose fitting and has an air nipple on the other end. REMEMBER to open the black tank drain valve when doing this, otherwise you may damage the system!!!
Blowing it out is the way to go but how would the system be damaged; the black tank is vented.
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Old 09-22-2018, 08:46 PM   #6
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Blowing it out is the way to go but how would the system be damaged; the black tank is vented.
If you read the instructions regarding flushing the black tank, the drain valve must be open to avoid damage to the system.
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Old 09-22-2018, 09:09 PM   #7
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So it turns out that the threads on the outside shower wand is 1/2 NPT.

I just bought a 1/2 NPT to hose male adapter at Home Depot and connect it to the black flush (using a check valve not shown) during winterization.

When I winterize the shower I also do the black tank flush.
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Old 09-22-2018, 09:38 PM   #8
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So it turns out that the threads on the outside shower wand is 1/2 NPT.

I just bought a 1/2 NPT to hose male adapter at Home Depot and connect it to the black flush (using a check valve not shown) during winterization.

When I winterize the shower I also do the black tank flush.
Good info for the folks with your model type, but there is no outside shower or shower wand on the Mercedes Benz chassis RV being discussed in this particular forum.
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Old 09-22-2018, 09:44 PM   #9
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Good info for the folks with your model type, but there is no outside shower or shower wand on the Mercedes Benz chassis RV being discussed in this particular forum.
Gotcha. Sorry.
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Old 09-22-2018, 10:12 PM   #10
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If you read the instructions regarding flushing the black tank, the drain valve must be open to avoid damage to the system.
The flush system on any RV canít in itself cause damage because the black tank valve is closed. I usually close mine for 5 minutes and then reopen to allow the tank to partially fill to get a good flush. The damage comes if you get distracted and walk away with the valve closed and the black tank overfills. Now, being that it is vented the overflow should come out on your roof. I donít want to find out so I always set my iPhone timer to remind me when it is time to open the valve.
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