Blackwater tank "full of it" - Fiberglass RV

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Old 10-05-2015, 10:35 AM   #1
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Trailer: Bigfoot 17 ft Gaucho
Posts: 145
Blackwater tank "full of it"

my 17 foot 2005 Bigfoot has repeated problems with the valve sticking on the black water tank. Repaired the first time -- that didn't work. Last time the valve was replaced. Next trip out, I took it to the Northern Oregon Gathering last weekend, and again it won't drain. What could possibly be wrong and what should I tell the repair people (who usually are very knowledgeable).

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Old 10-05-2015, 11:31 AM   #2
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Name: Jack L
Trailer: Bigfoot B-17 CB
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My experience with these things is that they work until they don't work. It's a rubber seal and if it gets damaged or some solid material gets stuck in it, it needs to be disassembled and replaced or cleaned and lubed. First I would check the stainless steel shaft on the T handle. No disassembly required for that and try to lube it. The valve itself is probably less than $25 and it's not difficult to replace, but is sure is messy. To clean and lube the valve you need to remove it and if it were mine I would most likely replace it. The only thing you can do is be careful what you flush and cross your fingers.

If the valve opens and closes easily and does not leak, it's ok and does not need any service. Next I would check for obstructions. Might be some paper product clogging the discharge . I've seen s toothpick clog a pipe and I've also seen a small burr on a fitting snag something causing a clog. If this is the case you would need to find the issue that's causing the clog. A solution could be as simple as changing the brand of toilet paper you use or using as little TP as possible, or as complicated as disassembling the piping (cutting) if it is something solid is the issue. There are some adaptors you can purchase to put on in place of the discharge cap so you can backflush the system and that's worth a try before you start cutting pipes. If you do this yourself, don't bite your fingernails !

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Old 10-05-2015, 11:50 AM   #3
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thanks for your suggestions.
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Old 10-05-2015, 11:56 AM   #4
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Trailer: 1973 Hunter Compact II
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I'm only guessing that the valve blade is actually opening, but that the tank isn't draining. Based on that: (Spoiler Alert!!! Yucky Questions Ahead....)

What comes out if the tank is full and the valve opened? How about when the valve was removed?

I have seen the following problems, usually in RV's that had enjoyed several past owners:

1. Balled up toilet paper blocking the tank drain. Some of the "Softer/fluffier/quilted etc household brands do not dissolve well and can block tank drains.

Consumers Reports recently found that "Scott Extra Soft" is the fastest dissolving TP. We started using it in a very old line that often got backed up and it seems to flow a lot better now.

2. Loose piles of "Stuff". If a tank was left with solids in it for an extended period of time, it will harden and build up into a pyramid in the middle of the tank. This, in turn, can break loose and take up residence at the drain opening from the tank or in the drain line itself. There are some cleaners that claim to reduce this stuff if soaked for several days at a time.

3. Improper use. I have come across a few tanks that the current or previous owners had used the black tank for "other" stuff, such as potato peels, paper towels, ladies sanitary products, fat from frying pans and, in one case, a soiled bath towel.

If practical, you might have a regular plumber use a scope (TV camera on a flex line) through the toilet opening to find out what's really down there. Even an inspection mirror on a stick and a flashlight might reveal the issue.

Bottom line, when drained and cleaned, the inside of the tank should look, except for stains, "Like New".
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Old 10-05-2015, 01:45 PM   #5
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We used a product designed for cleaning clogged cesspools ,and septic distribution boxes & drain fields in our Scamp . Add the product to the black tank and let it work for about a week.
The product is designed to dissolve solids ,paper and grease . There is an odor when the product is working but still less messy and stinky than snaking out the drain line.
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Old 10-06-2015, 08:49 AM   #6
Name: Lee
Trailer: Casita
Posts: 33
One rv we had had similar problems. I put lots of water in the black tank and let it sit for s day, then dumped in some dawn dish soap, a good healthy squeeze and a bag of ice. Then took the trailer for a nice ride. The ice I. The water agitates and bangs around in the tank and really knocked stuff loose, and it drained just fine. I also have one of those wands that hooks onto the water hose, you poke it down into the opened drain hole in the bottom of the toilet and blast away, every single time I dump the the tank. You can actually see the bottom of the tank when it is clean as it is clear/white plastic and light shines through. As long as I clean it every time without fail and don't let anything sit in it, it is easy to clean. And no valve problems.
I also put some water back in the tank rather than leave it empty, along with some of the digestor product. Never a standing nasty stuff.
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Old 10-06-2015, 08:58 AM   #7
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Name: Darral
Trailer: Scamp Standard 13' 2010
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That valve can cause some GREAT embarrassments at campgrounds. I wouldnt fight it- I'd replace it and be done!

EDIT: I see where you said it WAS replaced.... I agree with Roger...sounds like it needs some lubrication....OR you have some mighty strong "acids" in the tank that is enlarging the seal almost instantly causing it to swell the rubber seal thus making it next to impossible to open.

...sounds like your tank may need some EXTRA EXTRA cleaning!!
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Old 10-06-2015, 09:12 AM   #8
Name: Loren and Debbie
Trailer: In the market
Posts: 35
We had a Flagstaff a year ago. Had same problems with draining. Took it to the shop and it had roots in it! They said they had never seen that before! It was a new trailer so somehow the plants got in the tank before it was installed in the trailer. They cleaned it out and put root killer in it. No more problems
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Old 10-06-2015, 10:42 AM   #9
Name: RogerDat
Trailer: 77 Scamp 13
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+1 on dump in a bag of cube ice and take it for a drive with tank half full of water/solution & dish soap. The ice cubes do a great job of "scrubbing" out the tank and will break up most things that could be a blockage.

Lubrication of the valve should be attempted too.

Have heard of folks that hook up to park sewer then leave the valve open. Very bad! allows solids to build up since all liquid drains off and solids left behind can create blockage. Proper is to allow tank to fill part way then drain by opening valve.

Am puzzled OP says "valve was replaced" still won't drain? That either leaves blockage inside or the cover is still on the outside. Pulling that T out handle should pull back the valve blade and leave a 4" opening that is pretty hard to block.

Only other thought I had was don't some toilets have an internal tank that has to be dumped to the external tank? An extra step, but the set up allows one to recycle the interior toilet tank until full like a porta pottie then dump to the external black tank. Increasing the useful capacity of the external tank.

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