Black Tank Flush System Issue

[barnbnb]

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

[barnbnb]

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.

[youroo]

Originally Posted by barnbnb

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! !

[barnbnb]

Originally Posted by youroo

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!!!

[bubbles]

Originally Posted by barnbnb

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.

[barnbnb]

Originally Posted by bubbles

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.

[Herk7769]

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.

[barnbnb]

Originally Posted by Herk7769

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.

[Herk7769]

Originally Posted by barnbnb

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.

[dalford]

Originally Posted by barnbnb

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 can’t 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 don’t want to find out so I always set my iPhone timer to remind me when it is time to open the valve.

[Herk7769]

Originally Posted by dalford

The flush system on any RV can’t 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 don’t want to find out so I always set my iPhone timer to remind me when it is time to open the valve.

A word of caution.

Water dropping in by gravity does not generate the pressure that the turbo flush can. Once the tank fills to the vent, it will pressurize the tank to force the water up the vent pipe.

The tank is more likely to burst before much water exits onto the roof.

[dalford]

Originally Posted by Herk7769

A word of caution.

Water dropping in by gravity does not generate the pressure that the turbo flush can. Once the tank fills to the vent, it will pressurize the tank to force the water up the vent pipe.

The tank is more likely to burst before much water exits onto the roof.

Maybe? I think those tanks are pretty resilient and I know it will blow out the vent because I watched RV with Robin Williams..

So the real point here, either way, is you can close the black tank valve while flushing (I and most everyone I know does it) just don’t allow it to overfill. If you do one way or the other you are going to have a mess on you hands, shoes, back..lol...

[Herk7769]

The principles of risk management dictate that if the risk of failure is low, but the failure would be catastrophic, avoid the risk.

I also close the valve and let it fill while dump flushing. However, I only do that for 30 seconds or so while I am standing (kneeling?) there.

I would rather do that several times, than once and take a chance of bulging the tank and/or breaking a support or seam.

Just me though ...

[ICanFixIt]

I think I'm missing something here. I don't understand the benefit of leaving the drain closed while flushing the tank. I leave my drain open while flushing with the thought that the flush is a jet in the side of the tank that cleans by hitting the sides and bottom of the tank with a jet spray. If I leave the drain closed then the tank fills with water and covers areas of the tank that the jet cannot hit. For a thorough tank cleaning, I fill the tank with water through the toilet so I can see the level and add some softener and let it soak for a day or two. Then flush as normal. Seems to keep my sensors working and does a real good job of cleaning of the tank. I would fear using the flush to fill the tank with the drain closed and pressuring the tank, at some point you're going to screw up and the water is going to come out of places you don't want like your toilet or toilet valve long before it will reach the top of your vent. Even if the tank holds the pressure and it reaches the top of vent, that is an ugly thought of the cleanup required and the surprise of how you found out it hit the vent (is it raining again?) What am I missing?

[JohnD10]

I also start the flush seconds after I pull the black plug drain.

That was it is washing the stuff down to the bottom of the tank.

I also backflow the gray water into the black tank while the tank flush is running.

In theory (mine, of course) that should also dislodge anything that might be stuck at the bottom of the black tank.

[Busybeavers]

Originally Posted by ICanFixIt

I think I'm missing something here. I don't understand the benefit of leaving the drain closed while flushing the tank. I leave my drain open while flushing with the thought that the flush is a jet in the side of the tank that cleans by hitting the sides and bottom of the tank with a jet spray. If I leave the drain closed then the tank fills with water and covers areas of the tank that the jet cannot hit. For a thorough tank cleaning, I fill the tank with water through the toilet so I can see the level and add some softener and let it soak for a day or two. Then flush as normal. Seems to keep my sensors working and does a real good job of cleaning of the tank. I would fear using the flush to fill the tank with the drain closed and pressuring the tank, at some point you're going to screw up and the water is going to come out of places you don't want like your toilet or toilet valve long before it will reach the top of your vent. Even if the tank holds the pressure and it reaches the top of vent, that is an ugly thought of the cleanup required and the surprise of how you found out it hit the vent (is it raining again?) What am I missing?

Well, I can say that I have seen the inside of my black tank. I have always closed the valve and refill the tank with the sprayer. In fact, I walked away and it overfilled, it did not come out the toilet, (because it is sealed), if it does then your seal is bad, it will not come out the vent pipe, too much pressure for the thin walled plastic tank, what it does is blows the tank, the insulation, and the black plastic panels from underneath. Mine split a gap from end to end. Thank heavens it was only water, because I was on the third rinsing. This did allow me to look inside the tank to see the condition of cleanliness of the tank. The tank was perfectly clean! But I did notice that the location of the sprayer on the end, can not hit all the surfaces to flush the entire tank. In fact in most cases, it will not even clean off the tank probes, thus why we all have trouble with the tank gauges. By flushing the tank several times (filling/draining and refilling/draining) it does wash the entire tank. You just have to be sure you don't forget about it and allow it to overfill. Or like me, you will be driving up to see Orvin Fry.
"Just my 2 cents and experience."

[kandl]

Originally Posted by ICanFixIt

I think I'm missing something here. I don't understand the benefit of leaving the drain closed while flushing the tank.

You'd be amazed at all the extra crap (pun intended) that flows out of the BWT by closing the gate valve for short periods of time while flushing. I was when I began employing this method some yrs ago. I don't advocate filling the tank completely via the flush but partial filling three or four times by closing/opening the gate valve is much more effective than the flush alone.

[High Desert]

Originally Posted by barnbnb

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.

Actually, On my 2017 FR Sunseeker MBS 2400R, I do have an outside shower that uses a quick disconnect system with a coiled hose setup. Haven't used it yet, but it's there if needed.

[barnbnb]

Originally Posted by High Desert

Actually, On my 2017 FR Sunseeker MBS 2400R, I do have an outside shower that uses a quick disconnect system with a coiled hose setup. Haven't used it yet, but it's there if needed.

That's a spray hose you have, not a shower. It's a totally different design than the hot and cold shower unit which the OP described. It would obviously not work on the MB chassis with the adapter fittings he described.

[barnbnb]

So anyway, back to the original point of departure: If you have the Mercedes chassis with the full wall slide, the bathroom is in the right rear corner.
Under the sink is the breaker/check valve.
Other models may have the bath in the same location.
My plumbing lines were not secured, so vibrations caused the fitting to fail.
To prevent breaking the barbed plastic "inlet to valve" fitting, make sure the plumbing lines are secured to a solid surface.
Happy Camping Y'all!