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nickthehunter

Southgate, MI

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Posted: 06/22/22 10:07am Link  |  Quote  |  Print  |  Notify Moderator

Why do people not leave their black tank valve open when flushing the tank? Valve open, tank won't overfill, why would I want to risk a disaster?

* This post was edited 06/22/22 10:18am by nickthehunter *

time2roll

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Posted: 06/22/22 10:35am Link  |  Quote  |  Print  |  Notify Moderator

nickthehunter wrote:

Why do people not leave their black tank valve open when flushing the tank? Valve open, tank won't overfill, why would I want to risk a disaster?
A lot more debris comes out with the rush of the filled tank draining again. The spray alone will not move a heavy wad on the bottom.

I find the sensors work fine to determine ~75% full and pull the lever. Takes real focus to avoid getting distracted. With some experience a timer could be set.


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Posted: 06/22/22 11:29am Link  |  Quote  |  Print  |  Notify Moderator

I think Cummins has made the right call and I believe you need a major cleaning sooner rather than later.


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cummins2014

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Posted: 06/22/22 12:39pm Link  |  Quote  |  Print  |  Notify Moderator

dougrainer wrote:

OK, one thing that can happen when you do this, it can BREAK the 3 inch down tube from the black tank. The Pressure involved when you do this is tremendous. 45 psi or more has filled the black tank and now the tank has expanded(swollen) and popped either the 3 inch down tube loose or the 1.5 inch vent tube loose. We know this because instead of water coming out the roof vent and overflowing on the roof it came out the bottom from the top of the tank. Because the tank broke open at the tank which is a good thing instead of out the roof vent. NOW, if you do NOT fix the problem on top the tank, you will have black tank odor migrating into the lower bottom cavity because it is NOT sealed now. The RVIA standard for both Gray and Black is to hold water when overfilled. With Black we fill until the water is just below the toilet ball valve and on Gray with water coming into the shower or tub. Also, unless you access and clean out the top of the tank and the underbelly and insulation, you will now have a musty smell all the time. Both inside and out. Doug


IMO that’s not the best way to tell if the black tank is full , for us is an air bubble forms when flushing , and that’s full enough for me . As far as letting it start filling the shower floor that may work for you , but the one time it happened to my wife while showering , she wasn’t that thrilled to be standing in the waste water . We know pretty much our usage on the gray tanks , and every three days or so I just pull the handles for a few seconds , and save enough when I do the black tank to flush the pipes a bit better , then I just empty all three, and start over .

dougrainer

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Posted: 06/22/22 01:21pm Link  |  Quote  |  Print  |  Notify Moderator

cummins2014 wrote:

dougrainer wrote:

OK, one thing that can happen when you do this, it can BREAK the 3 inch down tube from the black tank. The Pressure involved when you do this is tremendous. 45 psi or more has filled the black tank and now the tank has expanded(swollen) and popped either the 3 inch down tube loose or the 1.5 inch vent tube loose. We know this because instead of water coming out the roof vent and overflowing on the roof it came out the bottom from the top of the tank. Because the tank broke open at the tank which is a good thing instead of out the roof vent. NOW, if you do NOT fix the problem on top the tank, you will have black tank odor migrating into the lower bottom cavity because it is NOT sealed now. The RVIA standard for both Gray and Black is to hold water when overfilled. With Black we fill until the water is just below the toilet ball valve and on Gray with water coming into the shower or tub. Also, unless you access and clean out the top of the tank and the underbelly and insulation, you will now have a musty smell all the time. Both inside and out. Doug


IMO that’s not the best way to tell if the black tank is full , for us is an air bubble forms when flushing , and that’s full enough for me . As far as letting it start filling the shower floor that may work for you , but the one time it happened to my wife while showering , she wasn’t that thrilled to be standing in the waste water . We know pretty much our usage on the gray tanks , and every three days or so I just pull the handles for a few seconds , and save enough when I do the black tank to flush the pipes a bit better , then I just empty all three, and start over .


Did you NOT read what I posted? I was posting how a Service shop TESTS the Tanks on a PDI, NOT HOW to tell when tanks are full. Doug

way2roll

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Posted: 06/22/22 01:59pm Link  |  Quote  |  Print  |  Notify Moderator

nickthehunter wrote:

Why do people not leave their black tank valve open when flushing the tank? Valve open, tank won't overfill, why would I want to risk a disaster?


Because it's not only the force of the water from the flush to "wash" debris from the sides of the tank, it's the physics involved to use a 1/2 or 3/4 full tank's rush of water to flush all that debris out the hose. I repeat this process several times until I get clear water. The trick, as the op found out, is not to walk away and let it overfill. It's only a disaster if that happens.


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Cummins12V98

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Posted: 06/22/22 02:51pm Link  |  Quote  |  Print  |  Notify Moderator

time2roll wrote:

Step away like a boss. Nothing happened.


How do you know???


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Cummins12V98

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Posted: 06/22/22 02:53pm Link  |  Quote  |  Print  |  Notify Moderator

dougrainer wrote:

OK, one thing that can happen when you do this, it can BREAK the 3 inch down tube from the black tank. The Pressure involved when you do this is tremendous. 45 psi or more has filled the black tank and now the tank has expanded(swollen) and popped either the 3 inch down tube loose or the 1.5 inch vent tube loose. We know this because instead of water coming out the roof vent and overflowing on the roof it came out the bottom from the top of the tank. Because the tank broke open at the tank which is a good thing instead of out the roof vent. NOW, if you do NOT fix the problem on top the tank, you will have black tank odor migrating into the lower bottom cavity because it is NOT sealed now. The RVIA standard for both Gray and Black is to hold water when overfilled. With Black we fill until the water is just below the toilet ball valve and on Gray with water coming into the shower or tub. Also, unless you access and clean out the top of the tank and the underbelly and insulation, you will now have a musty smell all the time. Both inside and out. Doug


How do you know this? There is a roof vent there for a reason, I don't see how pressure can be added when there is a vent.

cummins2014

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Posted: 06/22/22 03:09pm Link  |  Quote  |  Print  |  Notify Moderator

dougrainer wrote:

cummins2014 wrote:

dougrainer wrote:

OK, one thing that can happen when you do this, it can BREAK the 3 inch down tube from the black tank. The Pressure involved when you do this is tremendous. 45 psi or more has filled the black tank and now the tank has expanded(swollen) and popped either the 3 inch down tube loose or the 1.5 inch vent tube loose. We know this because instead of water coming out the roof vent and overflowing on the roof it came out the bottom from the top of the tank. Because the tank broke open at the tank which is a good thing instead of out the roof vent. NOW, if you do NOT fix the problem on top the tank, you will have black tank odor migrating into the lower bottom cavity because it is NOT sealed now. The RVIA standard for both Gray and Black is to hold water when overfilled. With Black we fill until the water is just below the toilet ball valve and on Gray with water coming into the shower or tub. Also, unless you access and clean out the top of the tank and the underbelly and insulation, you will now have a musty smell all the time. Both inside and out. Doug


IMO that’s not the best way to tell if the black tank is full , for us is an air bubble forms when flushing , and that’s full enough for me . As far as letting it start filling the shower floor that may work for you , but the one time it happened to my wife while showering , she wasn’t that thrilled to be standing in the waste water . We know pretty much our usage on the gray tanks , and every three days or so I just pull the handles for a few seconds , and save enough when I do the black tank to flush the pipes a bit better , then I just empty all three, and start over .


Did you NOT read what I posted? I was posting how a Service shop TESTS the Tanks on a PDI, NOT HOW to tell when tanks are full. Doug


Yes , and your wording could of said what you just replied or been more clear . Go back , and edit that would help . Thanks .

dougrainer

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Posted: 06/22/22 04:59pm Link  |  Quote  |  Print  |  Notify Moderator

Cummins12V98 wrote:

dougrainer wrote:

OK, one thing that can happen when you do this, it can BREAK the 3 inch down tube from the black tank. The Pressure involved when you do this is tremendous. 45 psi or more has filled the black tank and now the tank has expanded(swollen) and popped either the 3 inch down tube loose or the 1.5 inch vent tube loose. We know this because instead of water coming out the roof vent and overflowing on the roof it came out the bottom from the top of the tank. Because the tank broke open at the tank which is a good thing instead of out the roof vent. NOW, if you do NOT fix the problem on top the tank, you will have black tank odor migrating into the lower bottom cavity because it is NOT sealed now. The RVIA standard for both Gray and Black is to hold water when overfilled. With Black we fill until the water is just below the toilet ball valve and on Gray with water coming into the shower or tub. Also, unless you access and clean out the top of the tank and the underbelly and insulation, you will now have a musty smell all the time. Both inside and out. Doug


How do you know this? There is a roof vent there for a reason, I don't see how pressure can be added when there is a vent.


I suggest you start a Black flush and let it go with valves closed. If the pipes to the tank are glued, you will have sewage water coming out the roof top vent. I HAVE NEVER DONE IT! I have FIXED quite a few that customers have done it. AND, if the 1.5 inch pipe is NOT sealed where it comes thru the outer roof deck, you will get water into the roof cavity. With water coming out from the interior ceiling panels and such. Doug

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