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Old 08-28-2011, 06:37 AM   #1
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Black tank question...

Not a great Sunday morning topic, sorry. We have 45 gallon black and gray water holding tanks. In my very, make that extremely, limited knowledge of RV's I wonder how much water one should use per flush. Even with showers and dishwashing etc, the black tank guage shows it fills faster than the gray. However, when dumping, the gray takes longer to empty. Also, what if any chemicals do you use in your tanks?

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Old 08-28-2011, 06:58 AM   #2
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Originally Posted by johnnyringo View Post
Not a great Sunday morning topic, sorry. We have 45 gallon black and gray water holding tanks. In my very, make that extremely, limited knowledge of RV's I wonder how much water one should use per flush. Even with showers and dishwashing etc, the black tank guage shows it fills faster than the gray. However, when dumping, the gray takes longer to empty. Also, what if any chemicals do you use in your tanks?
Use a lot of water in black tank (put water in after you have dumped and closed valve). You can always empty tanks as often as you want. Many RVs have smaller diameter lines for the grey tank than black tanks have, therefore it takes longer to empty the grey. Some grey tanks may also be larger than black tanks. Always empty black tank first, close its' valve the dump the grey tank (helps clean out the hose).

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Old 08-28-2011, 07:41 AM   #3
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Black and gray water tank discussions are always popular amongst RVers it seems. I've found a "load" (pun intended) of material within this site from chemicals to use in your BW tank to using Calgon to dumping a bag of ice in the tank to break things up while driving to the dump site.

For me, I keep it simple and use the Thetford products for BW treatment and do not mix brands. It may be rubbish, but somewhere along the line I was told that some brands don't "like" each other and mixing different brands can reduce their effectiveness. But I dump, flush, add a bowl or two of water with an 8 oz. bottle of that evil looking blue stuff and trust the chemistry.

I also have a back flush connection for my BW tank I use while dumping. NEVER allow your BW tank to be dry.

Some RVers have told me they use regular TP without any issues with the tissue. Me, I am strict about using the single-ply Thetford TP I can get at Wallyworld or Camping World and as I advise the Little Lady to "Be sensible" in its use. It's under the "penny wise; pound foolish" school to use the correct stuff for BW tank as I imagine having your tank de-funked and repaired will be pricey and some shops might refuse to work it.

As for gray water management, I'm been trying to convince the Little Lady that we should shower together as a water conservation measure. She's not buying it (I'm still trying though) but "Navy Showers" are routinely announced at Morning Quarters while boondocking. "Hollywoods" are grudgingly permitted with shore connections - but I allow the BW tank to fill to about 2/3's before it is dumped and leave the valve closed for odor control while in a park with full hook-up. Allowing the tank to fill more before dumping gives a better flush as the greater, longer flow entrains more "schtupf" on the way out. Another iRV2 tip I got here.

Some of these guys on this site with a bunch of campfires seem to have done it ALL at one time or another, so I come here for the same purpose: learn from their collective experience.

One more thing: fresh water weighs 8.3-lbs./gal.
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Old 08-28-2011, 07:51 AM   #4
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See this thread for what happens when you don't use enough water.
The Dreaded Black Tank 'Pyramid'

As to emptying speed, on my rig the black line is 3" in diameter & the grey is 1.5". The grey empties much more slowly.

We don't use any chemicals in the tank during the summer as we are living in the rig & they would never stay in the tank long enough to do any good.

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Old 08-28-2011, 08:01 AM   #5
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Typically, your Black Tank is smaller in capacity than you Gray Tank. Look up to see what your tank capacities are. I happen to have a 40 gallon black and 60 gallon gray. Depending on your usage rate I would think the gray would fill up faster than the black at least that's how it is our coach. I dump the gray twice as much as the black.

Most but not all gray tank dump valves are 1.5 inch valves versus 3 inch valves. Therefore it will take longer to drain because there is more gallons to dispose of and a smaller opening.

Why your black tank is filling so fast, only you can answer that as you are the ones putting the crap in the tank and filling it up.

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Old 08-28-2011, 10:17 AM   #6
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Tank level sensors are notorious unreliable. Don't trust them. Dump before you get a secondary indication other then a light.

Many many years ago I heard it said that the number 1 mistake rv'ers make is not using enough water when they flush. Become a firm believer in "solution by dilution" and practice it. Even when in a water conservation boondocking mode.

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