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Old 08-30-2014, 06:36 PM   #1
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Myth - Black Tank Drains Clear Water Means it is Empty

I see many posts that advise using a clear elbow when draining the black tank and to flush until the liquid runs clear. Supposedly this means the tank has been emptied. I subscribed to this theory for years.

However my current TT has proved this to be a myth, at least most of the time. I had issues with the black tank not reading empty, even with clear draining water. On the last two dumps, I sat next to the elbow and watched as I flushed the tank. I would notice that often when the liquid ran clear, the flow was reduced. So I would close the gate valve for a few minutes and reopen. Sure enough, a big chunk of TP would come out and then more waste. It appears that TP would get right in front of the drain and actually filter the water so it appears clear.

The only way to make sure the tank is empty, at least for me, is to make sure the flow is clear AND strong. I have found that it takes a good 20-30 minutes to properly flush and empty a black tank.

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Old 08-30-2014, 07:02 PM   #2
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I'd say the elbow isn't so much to see the liquid run clear as it is just to see what's going on.

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Old 08-30-2014, 07:32 PM   #3
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Originally Posted by rockfordroo View Post
I'd say the elbow isn't so much to see the liquid run clear as it is just to see what's going on.
My clear section is to see the liquid run clear. However; after initial dump I close the dump valve and fill the tank and then dump again. Takes about 20 min for the tank to refill from the cleanout port. If not clear after first time then I do it again till liquid runs clear. I know there is a warning to not close the valve with the cleanout active but that's hog wash. The indicator light will show an empty tank after this procedure and the tank will be as clean as can be. There are several on line videos showing how to empty a black water tank.
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Old 08-30-2014, 07:38 PM   #5
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We never just use the flush system alone. Usually when they're new, we time filling the tank with our water system at home, which is about the only place we actually flush and dump the tanks. Our procedure for dumping tanks is by innitially dumping the tank with the flush system running, close the dump valve and time filling the tank, dump, repeat etc etc. We do use the clear fitting as well. By using the flush system alone until it runs clear (tank valve always open), it will not get everything in the tank. By partially filling the tank each time, there is a better chance for the volume of water to carry the solids better. Some disagree with this method as they say you can overflow the tank. True, but, if you've done like me, and figured out the timing of the fill, and you DON'T get distracted and walk off, this method works very well.

I've played with these flush nozzles, several different kinds, and I assure you it will not clean that tank very well. They only hit parts of the tank, and you will in fact see clear water, yet still have stuff in the tank. I have installed additional flush nozzles in tanks before which proved a shade more effective.
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Old 08-30-2014, 07:43 PM   #6
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Originally Posted by itat View Post
Teamfour, have a look at these videos...
Those videos helped me develop my process and only prove what I stated. Thanks.
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Old 08-30-2014, 07:49 PM   #7
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For me, running the tank flush does not thoroughly clean the tank by itself. I heard somewhere the suggestion to close the drain valve while the tank flush is running to fill the tank (the manufacturer says DON'T do this!). This fill/dump will bring with it much debris that the original dump and the flushing process missed.

A couple trips ago I had full hookups and plenty of time. I performed the above (dump/flush/fill/dump). I then (for no particular reason) ran the flush with the valve open again and went for a bike ride. The ride ended up much longer than expected and the tank flush had been running over an hour by the time I returned. The water coming from the tank was clear and strong. I then for some reason closed the valve for a 2nd fill/dump, and to my surprise...a bunch more debris passed. I then was on a mission...went for a 3rd fill/dump, and it finally ran near as I could tell.

In short, using the tank flush to fill/dump the tank at least once and maybe twice is the only/best way to get a clean tank...IMO.

edit...sorry for the redundancy...I type slow!
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Old 08-30-2014, 09:05 PM   #8
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I think after watching the one video I will keep using Camco 40074 Flexible Swivel Stik Rv Tank Rinser because it can reach from one end of the tank to the other and get the most out.
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Old 08-31-2014, 08:50 AM   #9
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I used this one because it gives a stronger stream that I can aim all over the tank. Valterra A01-0184VP Master Blaster Tank Wand: Automotive
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Old 09-02-2014, 01:30 PM   #10
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I agree. From watching that video with the clear tank, you can really see that even a full tank of water does not really to that much to move the solids out. You need to spray directly in the tank and try to break it up into smaller pieces and get it to flush out.


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black, black tank, drain, tank, water

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