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Old 07-27-2013, 12:49 AM   #1
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Black tank dumping

HELP! I have been in discussions with my wife regarding or new RV and the black tank dumping intervals. She thinks we need to dump the tank when it may only be 1/4 or keep it low??? I believe that that we need to dump it when needed....3/4 but not letting it sit in the tank long. Or not dumping every two day stop just for the two of us? Can you assist with this topic? Thanking you in advance. First time RV'er


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Old 07-27-2013, 12:59 AM   #2
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I think you're going to find it a matter of personal preference. While I wouldn't let it sit for weeks, it shouldn't hurt to keep it in for a while with chemicals and what not. If you don't dump it, it'll add weight for you to carry around. If you do dump it every outing, fill it with the toilet or a flush connection if you have one until it's 3/4 full. That way, there's enough flow to flush out the majority of the stuff. Also, dump the black first, then the grey.

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Old 07-27-2013, 01:04 AM   #3
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Main thing is to use plenty of water when flushing and letting the tank get at least 2/3 full before emptying. If you have a black tank flush (separate hose connection), I turn it on while emptying to make sure things get stirred up a bit and leave it on until the discharge is pretty clear, then I close the valve and let the flusher run about a minute to insure there is water in the tank. Then I dump the grey tanks to clean the slinky hose. NEVER LEAVE THE BLACK TANK VALVE OPEN! You will get a mountain you don't want and it can possibly build up to the commode if the plumbing is just right and be extremely difficult to remove.
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Old 07-27-2013, 01:10 AM   #4
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The recommended dump is a full tank. Now that could mean you add more water to a half full tank to flush or you travel with the extra weight of a partial full tank. With proper maintenance you should not have odor from a partial tank but I do not leave the trailer sitting between trips with sewage in the tank. Do you have a tank flush system?

Helpful link to the Geo Method =
Several members use this and have no odor issues.

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Old 07-27-2013, 05:08 AM   #5
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We've found Walex Bio-Pak very good. Rather than just chemicals to mask the odor, it actually has enzymes that eat away at the solids (including paper). We live in the country and having septic tanks that operate on the same principal - and with just the two of us, it only takes a couple of packs for a week-long stay in the RV. Bio-Pak - Walex T01-11530 - Sewer Deodorizers & Treatment - Camping World

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Old 07-27-2013, 01:41 PM   #6
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newbies tend to freak out about the black tank.

as others said, it's best to allow the tank to fill as much as possible, before dumping. if you have to add water before doing this, then fine.

we have a 30 gallon black tank. it won't get near to full until 2-3 weeks of straight camping.
so, we wait until after a number of camping trips to dump, when it's convenient.
there's no need to dump after only a 3 day camping trip, unless you've got a tiny black tank.

of course, we have good tank additives so there's no smell.
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Old 07-28-2013, 12:01 PM   #7
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Smile Black Tank

I have a small tank 12 Gl still getting use to it seeing how long it take to fill it 3/4 full ,i wish rocwood had the gray tank in front of the black tank so it can run through the same slinky hose ,I have a Rockwood HW 296 ,2014 .
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Old 07-28-2013, 12:27 PM   #8
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We dump every five days. Currently in a permanent spot for 4 months, so trailer is not moving.

That interval works for us and if i can trust the sensors, they are about two thirds full.
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Old 07-28-2013, 12:42 PM   #9
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my wife knows not when I dump the tank, the everything outside of my coach is all mine. but I dump at 3/4 full
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Old 07-28-2013, 12:57 PM   #10
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Originally Posted by Dovetail View Post
i can trust the sensors, they are about two thirds full.
Great point.
Things to know about the sensors:

1) The "empty" light means there is power to the system and there is no electrical path from any level sensor to ground. A broken ground wire will always show "empty" regardless of level.

2) The 1/3 light means "not empty" This probe is mounted so low a single flush will turn it on (in my camper) OR there is a high resistance path to the ground probe (typically soap or slime on the tank wall).

3) The 2/3 light is actually about 1/2 tank full or there is a better conductive path to the ground probe (TP on one probe touching another or a "better quality slime")

4) The "Full" light is actually about 7/8 full or a direct short from any probe to ground. Sludge between the 1/3 probe and the ground probe will indicate "Full".

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black, black tank, tank

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