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Old 07-09-2016, 23:36   #1
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Black Water Holding Tanks

Hello there,

I have a blocked up black water tank. After following the previous thread on this subject I put 4 liters white vinegar in tank and let "work " for 3 days and then flushed. Seems to be working a little so closed off tank and put in 14 liters to give it a bit of a belt.
Question. Does anybody know how long vinegar like this will continue to react till it finishes its process?

Next step will be muratic acid at 12- 15% concentration. Again how long would one leave this solution in a plastic tank?
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Old 08-09-2016, 06:00   #2
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Re: Black Water Holding Tanks

Quote:
Originally Posted by Amaranth View Post
Question. Does anybody know how long vinegar like this will continue to react till it finishes its process?

Search for posts by Peggie Hall (PegHall) ref vinegar. Mostly she says it needs changing often, and it's not optimum for "repair" work, mostly better for "periodic maintenance."

She has also mentioned some other products. Sew Clean comes to mind (private branded by Raritan as C-something; CH =for Cleans Heads (or Hsses)? CL for Cleans Lines? something like that...)

I think she has also addressed appropriate dilution percentages and soak times for other acidic products.

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Old 08-09-2016, 06:30   #3
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Re: Black Water Holding Tanks

When it is that backed up, new hoses are in order. At least that is my vote. Trident / Shields 101/102 sanitation hoses are a great choice if they don't need to be too bendy. There are other options out there if you search posts from Peggy Hall or buy her (new) book. Just never use Trident / Shields 148!

Vinegar, as mentioned above and by Peggy Hall, is to keep the hoses from becoming this gunked up!


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Old 08-09-2016, 07:09   #4
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Re: Black Water Holding Tanks

How did you determine that the tank is "blocked up"? You can't pump the contents out?

Very often, holding tank problems are not the tank at all but the vent or vent filter if one is installed. You can't get anything out of a tank (or put anything into a tank) if air can't get in to replace what you are trying to remove or get out to make room for what you are trying to put in.

So, check to see if you have a filter in the vent hose. If you do, replace it with a new one or, better yet, replace it with a regular hose so you won't have to deal with clogged filters in the future.

Check the thru hull the vent hose attaches to. It's not uncommon for insects to nest here and clog the vent.

Finally, if you have access to the top of the tank, it's not terribly difficult to cut a hole in the top of the tank and install a screw in access fitting. Once you do this, you can clean the tank manually. It's not fun but it's effective.
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Old 08-09-2016, 07:47   #5
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Re: Black Water Holding Tanks

As others have said, vinegar will not solve your problem. But even if it could, I agree with rwidman...your problem is most likely a blocked tank vent. Tank vents on all tanks--water, fuel and waste--have two primary functions: they provide an escape for air in the tank displaced by incoming contents and they provide a source of air to replace contents as they're drawn out. If no air can escape the system becomes pressurized...creating back pressure that would explain why waste may be backing up into the bowl when you flush. If no air can be pulled into the tank by a pumpout or overboard discharge pump, the pump will pull a vacuum that won't allow more than a gallon or two be be pulled out.

The two most common locations for a vent blockage are the vent thru-hull and the other end of the vent line--that end of the hose and the vent fitting on the tank. So start by scraping out the thru-hull with a screwdriver blade, ice pick or whatever works. Knock out any screen...screens cause more problems than they solve or prevent. If that doesn't result in a gush of waste out the vent, open the deck pumpout fitting (be sure you're UPwind of it and have a hose at the ready) to relieve any pressure. Remove the vent line from the tank (warming it a bit with a blow dryer will make that easier) and scrape it and the fitting on the tank out.

And oh yes...take another bit of rwidman's advice: Get RID of any filter in the vent line! If a filter gets wet, the charcoal can swell up blocking the vent line.

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Old 08-09-2016, 13:08   #6
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Re: Black Water Holding Tanks

Get in the water and slide a kebab skewer up the holding tank discharge. Get ready to swim fast.......
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how long has this been going on and why wasn't I told about it earlier.....
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Old 08-09-2016, 13:37   #7
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Re: Black Water Holding Tanks

Peggie, you know where I learned most of what I posted, don't you?
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Old 08-09-2016, 14:42   #8
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Re: Black Water Holding Tanks

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Old 09-09-2016, 19:26   #9
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Re: Black Water Holding Tanks

While messing with your vent tubes, take what I think is also Peggie Hall's advice and enlarge them. She points out that these tube should do much more than prevent vacuum locks. They should actually provide positive ventilation. I believe she recommends vent tubes as large as 1", preferably two tubes, one on each side of the boat. I followed this advice and am very happy.
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Old 10-09-2016, 21:18   #10
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Re: Black Water Holding Tanks

Thank you all for your views and assistance.
It is a next weekend job so I have plenty of actions to address, especially the vent piping.
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Old 02-10-2016, 23:21   #11
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Re: Black Water Holding Tanks

Just to close off the loop on this one for others who may have a similar type of holding tank.

In the end it was not the breather , however it did have some waste in it,now cleared.

The actual waste hose from the head does not go externally into the top of the tank. It actually enters from the bottom of the tank and ( as I now realize ) has a riser tube inside the tank that takes the waste to the top of the tank for discharge into the tank.

This riser tube was blocked, I imagine now somewhere near the top. I managed to jam a flexible rod up the tube and have cleared it so the heads now operate.

This internal tube has a 30 mm inside diameter so I am in the process of getting a flexible hose with a threaded end to which I will, in order, screw on a number of tuned up discs at say 20 mm 24 mm 27 mm and 29.5 mm slowly scraping the build up off this internal, inaccessible riser tube.

Hope this helps anybody else who finds themselves with such a tank. PJ
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Old 03-10-2016, 04:27   #12
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Re: Black Water Holding Tanks

Ugggh that's an awful setup!!


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Old 03-10-2016, 08:59   #13
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Re: Black Water Holding Tanks

The actual waste hose from the head does not go externally into the top of the tank.It actually enters from the bottom of the tank...

The inlet fitting must be moved to the top of the tank or you'll always have problems with it. It's not that hard to do, thanks to a li'l gizmo called the Uniseal (this link is to their US source, but they're an Australian company--Australian Global Services--so you should have no trouble finding them there.
UNISEAL Warehouse Seal the existing inlet with a threaded plug wrapped in plenty of teflon tape.

...and ( as I now realize ) has a riser tube inside the tank that takes the waste to the top of the tank for discharge into the tank.

That's an excellent way to do it because it prevents standing waste in the discharge hose. Your tank should be thoroughly flushed out with plenty of clean fresh water to remove any sludge. Using a bacterial tank product will help to prevent sludge and also buildup in the pickup tube.

All this is a bit of work going in, but should be very easy to maintain once you've done it.

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