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Old 11-30-2020, 02:14 PM   #1
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Black Tank - reduced capacity and how to fix?

Hi all,

I believe I have a decent amount of build-up inside my black tank. When the rig was new, the better half and I could easily make it 9 days without having to dump. Recently we noticed we are only making it 4 or 5 days, even while being conscious of extra water and paper going in.

I have run a few cycles of the 'geo method', and dropped a Bio-Active septic "pod" and 2/3 tank of water after my last dump. I figured I'd let it soak for a week before dumping...

Is there something else to be done to break up (what I assume is) a bed of solids on the bottom of the tank so I get my full capacity back?

Just me, my girlfriend and our crazy Boxer Stella.
'13 GMC 1500 Sierra Denali, '14 Stealth SS1913, '08 YFZ450 with some crazy engine mods.
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Old 11-30-2020, 02:49 PM   #2
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Try getting the tank 1/4 full of water, put in 1/2 a cup of Borax (20 Mule Team) and 1/4 cup of dishwashing detergent, drive it a good distance, such as to your next campground. We've switched to Borax exclusively and had no issues anymore. Also referred a good friend to this method and he reports the same.

You mentioned the "Geo method" and I did not know it was called that, so sounds like you are already trying this.

Do you have a black tank spray? If not you can get a wand you put down the toilet to break up your pyramid.
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Old 11-30-2020, 03:14 PM   #3
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I bought a used trailer back in the 70's that had been placed in an RV park and lived in. Black tank was apparently left open and the tank had a dried on layer of solids built up on the bottom. Tried everything to get it loose and flushed out.

Only thing that eventually worked was half a bottle of Dawn and three 5-gallon buckets of the hottest water I could get from the house water tank poured down the toilet. I let it soak for a couple days then towed it to the nearest dump station. Dumping 5-gallon pails down the toilet rather than trying to use the small dump station hose started to get "chunks" of the layer going down the dump hose. The bucket method provides a lot more flushing action than event the wand for buildup, especially that below the toilet.

From then on I started to use tank chemicals regularly and settled on the Odorlos as my "preferred". No issues anymore.

To add, it's important to dump while the tank contents are still liquid. Letting things sit for any length of time, especially in hot weather can reduce the amount of liquid and let solids settle where they can form a concrete like mass.

When that happens often it's necessary to go in through the dump valve with a long wand attached to a pressure washer to break it loose. I've also seen people with long pieces of PVC pipe doing this attached to a hose. The pipe is capped and holes drilled in the side so it sprays out in all directions hitting sides, top and bottom. The throught the toilet wands usually only hit the sides and ends. If the dump tube extends any distance into the tank that prevents it from hitting the top and limits the angles so the bottom isn't really sprayed where the buildup is worst.
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Old 11-30-2020, 03:21 PM   #4
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I'd get one of the black tank sprayer with the spinning head.
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Old 12-01-2020, 01:50 PM   #5
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The build up is likely directly under the toilet. Bad as it sounds, I’d use my pressure washer with a cardboard back splash scatter shield. Good time to use a full face shield and rubber gloves.
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Old 12-02-2020, 06:23 PM   #6
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Thanks all - I have a high-pressure water hose that I sprayed down into the toilet in an attempt to break down what may be there. I am still 'soaking' the tank with the septic drop-in and will be at a campsite this weekend where I will dump, flush and repeat a few times. Thanks again for the advice all.
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Old 12-02-2020, 07:04 PM   #7
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Are you certain that the tank is actually backed up or are the sensors not working properly?
You might want to add some Calgon Water Softener to the mix. That makes the sides slippery so that the stuff won't stick. (Walmart laundry section has it.)
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