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Old 06-23-2021, 07:42 AM   #1
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Stupid question Black tank.

I'm still learning about the Black Tank service. Is there a general rule of thumb on the percentage of fresh water, you should put into a black tank after it has been completely dumped and rinsed? IE 40 gal tank put 10% = 4gal water and chemical in?
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Old 06-23-2021, 07:58 AM   #2
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Frankly I don't. Unless it is going to be sitting for a while. While travelling there is enough liquid to keep everything sloshing around.

I will when hooked up and we are sitting for days. A couple of gallons but remember you can't add too much. Just leave room for poop!

There is no real rule of thumb. A few gallons will assist with dumping and you will soon know how much you need.
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Old 06-23-2021, 08:01 AM   #3
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After flushing the black tank, I will shut the valve off for a minute to accumulate water and then reopen the valve to flush again. I'll do that 2 or 3 times. When the liquid has cleared up, I shut the valve while still running the flush water in for a couple minutes. After I disconnect and clean the hose, I go inside, add chemical and flush two bowls of water. I don't know how much fresh water this process adds, but it has worked for 25 years with no buildup of solids.
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Old 06-23-2021, 08:15 AM   #4
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Thanks Guys
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Old 06-23-2021, 08:21 AM   #5
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After I flush the tank well and close the valve I leave the water run into it for a minute or two. Twenty plus years, no chemicals just water Zero problems.
Jeanie, Ed & Slade the GSD
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Old 06-23-2021, 08:25 AM   #6
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If I have to empty the tanks while in the middle of a camping trip, after emptying the tank I'll fill the toilet bowl twice and put that into the black tank. On the last emptying of a trip, when the RV is expected to be sitting for a while, I'll fill the toilet four or five times and leave that water in the tank. Like Cousin Ed above, I've found that with using plenty of water there is no need for chemicals.
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Old 06-23-2021, 09:14 AM   #7
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Dump when full
2X toilet bowls back in
No chemicals required

No Flushing required either...just a bell/whistle selling point
It's a holding tank.....holds waste (black or grey)
Dump when FULL....WHOOSH Effect
Add enough water back in to keep bottom wet
Vents/vapor barriers control odors

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Old 06-23-2021, 09:45 AM   #8
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I have a flusher for the black tank. After I'm finished flushing I close the tank valve and let the flusher run for about a minute. Don't know how much water that is but haven't had any problems!
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Old 06-23-2021, 09:46 AM   #9
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On mine it would probably take close to 5 gallons to fill the drain line to the dump valve. If you're trying leave some water on the bottom of the tank don't forget about that.
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Old 06-23-2021, 12:16 PM   #10
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More than 25 years here and have never left water in the tank after a dump. I figure things could dry out after a long while but we use the rig enough for that not to ever happen.

My technique is even easier than KISS. Have enough liquid before dumping, open black valve, dump, open gray valve, dump, close both, wash hands, and leave. Takes all of 2 minutes for me to do the duty.

Ours does not have a flush doodie dad. Even if it did, it would never be used by me. Totally unecessary in all the rigs we've ever had. A big irk for me is getting behind somebody at the dump station who flushes, empties, flushes, etc, etc, for 30 minutes,, arrgghhh!
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Old 06-23-2021, 02:25 PM   #11
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Always top off our black tank to over 3/4's full before heading to the dump station for adequate liquid sloshing around. We do black tank rinse if no one behind us, as well a full clean fill and dump every third time, mainly as we find this combination keeps our sensors cleared to read correctly.

Two flush bowls clean water, no chemicals, and adequate liquids/water when flushing during normal use.

Worked well for us with no piles ever since the 1990's on two rigs owned.

You'll get a feel over time what works best for you. FWIW: We also when putting in storage leave a good amount of fresh water and a little softener/dawn liquid in both the grey and black tanks, hoping it helps keep things smooth in there! Likewise we keep some water (antifreeze in winter!) in the toilet bowl for the seal to stay moist and top up as needed on inspections.
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Old 06-23-2021, 05:29 PM   #12
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Originally Posted by Cousin Ed View Post
After I flush the tank well and close the valve I leave the water run into it for a minute or two. Twenty plus years, no chemicals just water Zero problems.
Good advice
How much I add depends on situation...
If at full hook up I will add more water, up to maybe a 1/4 tank. If not planning on FHU site in next week I,ll add about 5 gals or so.
I dont use chemicals other than some soap / detergent prior to storage and periodically if trip is multi months.
Plenty of flush/ rinse is the best medicine
Don & Marge
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black tank, tank

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