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Old 11-12-2019, 08:18 PM   #1
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Black Tank Design Flaw

2020 Mirada 37RB.

We are staying in the motor home for the winter. We are having problems with the black tanks. They are backing up into the toilets when the tanks are less than half full. We have had RVís for decades so we know to put plenty of water in the tanks to help prevent the Pyramid of doom, but it is happening anyway.

From what I can tell there are 2 things that come together to create this problem; First is the tanks are shallow so it takes a lot of gallons of water to cover the bottom, let alone be enough to distribute the solids, consequently the solids build up under the toilet inlet quite easily. The second problem is that both of the toilets are on the right side of the motor home and the outlets are on the left side of the motor home so when the tank is dumped the liquids do not pass by the solids that are built up under the toilets. The black tank flush takes quite a while to clear the deposits, dumping a bucket of water down the toilet seems to work to get things to clear.

Has Anyone else had this issue and found a good solution?
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Old 11-13-2019, 01:10 PM   #2
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Sounds like you're not using enough water after the 'fact'.

Have you thought about trying the Geo Method of tank maintenance? It might help with the issue as it helps keep 'stuff' from sticking to the tank surfaces.
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Old 11-13-2019, 01:22 PM   #3
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Originally Posted by Bama Rambler View Post
Sounds like you're not using enough water after the 'fact'.

Have you thought about trying the Geo Method of tank maintenance? It might help with the issue as it helps keep 'stuff' from sticking to the tank surfaces.

I am sure we are using plenty of water. It also does not seem to be a problem of sticking to the tank. These tanks run the full width of the motor home so they are very very shallow, maybe 4 or 5 inches tall so it takes 15 or 20 gallons of water to put a couple of inches deep in the tanks. It appears there is just not enough water depth for the solids to move around in the tanks unless the motor home is in motion, and we are set for the winter so movement is not going to help like it does on shorter trips.
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Old 11-13-2019, 06:17 PM   #4
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We had the same problem with out coachmen pursuit 31SB. the problem was that the tank was shallow to go across the frame and then dumped into a deeper tank on the left side of the rv. So if you put a several gallons of water into the tank it would just settle on the left side. the result was the toilet paper and the solid waste would build up while the liquids would run into the deeper section of the tank.. The final solution for us was to have a macerating toilet installed. Coachhmen agreed to pay for the new toilet because of defective design. We have had zero problems to this date.
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Old 11-14-2019, 08:42 PM   #5
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toilet problems

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Originally Posted by DaveandChris View Post
We had the same problem with out coachmen pursuit 31SB. the problem was that the tank was shallow to go across the frame and then dumped into a deeper tank on the left side of the rv. So if you put a several gallons of water into the tank it would just settle on the left side. the result was the toilet paper and the solid waste would build up while the liquids would run into the deeper section of the tank.. The final solution for us was to have a macerating toilet installed. Coachhmen agreed to pay for the new toilet because of defective design. We have had zero problems to this date.
I am still waiting for Coachmen/ Forest River to step up and fix my toilet in the 30FW Pursuit? Wrote two different people at FR that were recommended on this site. Never so much as got a reply? Not good for word-of-mouth recommendations.
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Old 11-15-2019, 12:59 AM   #6
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Lightbulb

If you and your family each eat a bout 2 cans of beans at every meal you won't ever get the "Pile of Doom" syndrome and problem! Problem solved!
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Old 11-15-2019, 01:37 AM   #7
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Always more ways to skin a cat than one as Grandpaw Richard proves I guess ;-)

Definitely sounds like a design flaw on the depth of the tank. If your unsuccessful in getting manufacture assistance, my thought would be to tap into the cold water line that feeds the toilet and put a spray hose hanging on the wall behind it. I've actually seen these on some models to give you a little more force to rinse the bowl with and it sounds like it might do the same trick the bucket of water down the bowl is doing at a much lower cost that replacing the toilet or tank would. Just a fairly inexpensive solution I would try first if I were in your situation. Good Luck.
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Old 11-15-2019, 08:34 AM   #8
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If you and your family each eat a bout 2 cans of beans at every meal you won't ever get the "Pile of Doom" syndrome and problem! Problem solved!

That sounds like a case of the solution being worse than the original problem.


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Always more ways to skin a cat than one as Grandpaw Richard proves I guess ;-)

Definitely sounds like a design flaw on the depth of the tank. If your unsuccessful in getting manufacture assistance, my thought would be to tap into the cold water line that feeds the toilet and put a spray hose hanging on the wall behind it. I've actually seen these on some models to give you a little more force to rinse the bowl with and it sounds like it might do the same trick the bucket of water down the bowl is doing at a much lower cost that replacing the toilet or tank would. Just a fairly inexpensive solution I would try first if I were in your situation. Good Luck.
There is already one of those sprayers on the wall, it works to rinse the bowl when needed but does not have enough force or flow to help with the buildup in the tank.
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Old 11-15-2019, 08:51 AM   #9
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This seems like a stupid problem for an owner to need to deal with, particularly with the cost associated with these vehicles. If you have had success with the bucket of water method, perhaps your answer is to put a few gallons in the bucket. When you finish, dump the bucket as a final step in the process. You will be forced to dump more frequently, another added annoyance, but that might be your answer, unfortunately.

I have also always wondered to myself, why the f*** is the tank opening (pipe location where the tank contents flows when dumping) are on one end of the tank, rather than in the middle of the tank. This would require the tank to slope from all walls toward the center and down into a pipe that then exits the tank... Maybe its a ground clearance issue? So the edges of the tank might be 10" deep (I'm just making up numbers here), and the center might be 14" deep. Everything, liquid, solid, paper, etc would have an easier path to vacate the tank.

My above thought is very simplistic, and there would certainly need to be more thought put into it, as in, the ideal scenario is to have the toilet directly above that exit pipe, and since toilets are rarely in the center of the RV, you would need custom tanks with that exit pipe sometimes in the center of the tank, sometimes toward one end of the tank, etc. Just my thought. The RV industry relies on gravity to dump the tanks, but they only slope the pipes, not the tank bottom... And a shallow tank is going to be even worse... Maybe I need to be in the custom gray/black tank business, lol
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Old 11-15-2019, 09:14 AM   #10
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I have also always wondered to myself, why the f*** is the tank opening (pipe location where the tank contents flows when dumping) are on one end of the tank, rather than in the middle of the tank. This would require the tank to slope from all walls toward the center and down into a pipe that then exits the tank... Maybe its a ground clearance issue? So the edges of the tank might be 10" deep (I'm just making up numbers here), and the center might be 14" deep. Everything, liquid, solid, paper, etc would have an easier path to vacate the tank.

My above thought is very simplistic, and there would certainly need to be more thought put into it, as in, the ideal scenario is to have the toilet directly above that exit pipe, and since toilets are rarely in the center of the RV, you would need custom tanks with that exit pipe sometimes in the center of the tank, sometimes toward one end of the tank, etc. Just my thought. The RV industry relies on gravity to dump the tanks, but they only slope the pipes, not the tank bottom... And a shallow tank is going to be even worse... Maybe I need to be in the custom gray/black tank business, lol

These folks beat you to the punch on your custom gray/black tank business as they can make about any configuration of tank required. The bottoms of all the "holding" tanks they show are sloped.



https://www.alphallc.us/tanks/
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Old 11-15-2019, 09:41 AM   #11
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These folks beat you to the punch on your custom gray/black tank business as they can make about any configuration of tank required. The bottoms of all the "holding" tanks they show are sloped.



https://www.alphallc.us/tanks/
A day late and a dollar short... Bummer. Guess I need a new master plan.
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