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Old 07-31-2018, 09:46 PM   #1
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Default Best way to empty gray and black tanks?

What is the best angle to empty tanks vehicle facing uphill or downhill?

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Old 08-01-2018, 12:25 AM   #2
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I wouldn't worry about the angle since most dumping stations are fairly level. Plus, you really have no practical choice but to pull up on the side your dump valves are on (usually driver's side). Black & gray tanks usually converge from opposite ends (favoring one or the other, but not both). I guess I'd favor slope away from the black tank as the most preferable. Look underneath to find which way it drains to the valve.

But, just use the common procedures such as
- Don't put items (other than septic-safe paper) down your toilet.
- Use a suitable chemical in your black tank as well as add a gallon or so of water after dumping so your tank never gets dry.
- Try and dump when your tanks are at least half full (preferably more) to give you sufficient "whoosh" when dumping.
- Driving around just prior to dumping helps loosen the poo.
- Dump black tank first, close valve, then gray tank to flush out your dump line.
- Make sure your valves are closed, lines capped, hose stored, and compartments are latched shut.
- Oh, and keep disposable gloves handy you can wear during the process.

If you're really fastidious, and your rv has a santi-flush feature, you can give your black tank an additional flush with pressurized water (using a non-potable garden hose hooked up to a water source). But read up very well before using this feature first. You must have you black dump valve open to release the water as fast as it comes in! If you have a macerator pump, it must also be on. You don't want a nasty accident.

I would just conclude with, don't over-think it. You'll probably find that it's as simple as dump when there is sufficient liquids in the tanks and always black first, shut that valve, and pull your gray tank valve last, then close and store your hose.

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Old 08-01-2018, 04:28 AM   #3
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I could add to the good response you already got, when I dump at home into my sewer line cutout, the hose goes uphill. Well, my property is fairly level but the drive slopes toward the street..away from the cutout. So I connect up, open the black and "walk" the line (I lift it c. one foot) back to the cutout. Then I hose flush the black through the toilet (my only option). Walk that back. Then wait a while for anything to drip out, close the valve. Open grey water and repeat. I've actually started to flush the drain lines of the sinks by putting a hose with a valve on the end into the sink drain(s) and then opening it, producing a burst of water down the drain. Walk that back and close the grey valve.
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Old 08-02-2018, 09:13 PM   #4
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I like dumping my black tank first, then gray, then emptying the remnants of the fresh water tank into the black and gray (1/3 black, rest gray), just to ensure everything is rinsed. Then after that is done, I go to the potable water spigot and fill up the fresh water tanks.
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Old 08-03-2018, 06:04 AM   #5
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Every once in a while we Iím at a dump station that is not busy I take the time to fill both the black and grey a second time with the water provided. Then dump a second time to flush the tanks really well.
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Old 08-03-2018, 01:10 PM   #6
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Originally Posted by TC8 View Post
What is the best angle to empty tanks vehicle facing uphill or downhill?
It depends on your rig's tank configuration. On my RT, the outlet for the gray tank is at the rear of the tank and at the front of the black tank. My preference would be to get the black tank emptied, thus a need to face more downhill and of course sloped towards the driver's side.

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