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Old 01-12-2022, 12:16 PM   #1
Mini-Skoolie
 
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Using black tank as overflow for gray

Current build info is here for me - https://www.skoolie.net/forums/f11/p...ted-35906.html

My plan is to have all tanks on the driver side, gray tank stacked above black. My white tank is 80 gal, and I have identical black/gray tanks, 40 gal each. I know that gray will faster and am looking for a solution. Hoping an overflow pipe at top, run to the black below (with a hepvO valve to stop smells) should accomplish this. My rough brainstorm in image below. Any concerns or things I'm not accounting for with this?

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Old 01-12-2022, 01:11 PM   #2
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Without real world experience yet, the extra added time between tank draining that you might realize would likely be negligible for the added engineering and materials needed?

You can get a portable, wheeled, caddy to grain gray or black tanks into if one fills up before the other is ready to dump.

But if you have the ambition for such a project, more power to you...
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Old 01-12-2022, 01:21 PM   #3
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The only pitfall I can see is where your inlets to the grey tank are. If they're too low, you'll start backing up drains before it hits the overflow into black.
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Old 01-12-2022, 03:08 PM   #4
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Originally Posted by Dbacks2k4 View Post
The only pitfall I can see is where your inlets to the grey tank are. If they're too low, you'll start backing up drains before it hits the overflow into black.
From the drawings it looks like the tanks will be under the floor so any backing up in drain lines is going to be miniscule since the highest the overflow can be is the underside of the floor minus top of tank thickness, minus space between floor and top of tank.
The more likely cause of problems will be line routing to ensure free flow from the gray to black tank.
Considering the tanks available (and pricing) We're considering a similar set up for our black tank (though with stacked standard black tanks) to give a higher black tank capacity without buying expensive custom tankage.
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Old 01-12-2022, 03:59 PM   #5
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Originally Posted by HamSkoolie View Post
... From the drawings it looks like the tanks will be under the floor so any backing up in drain lines is going to be miniscule since the highest the overflow can be is the underside of the floor minus top of tank thickness, minus space between floor and top of tank.
The more likely cause of problems will be line routing to ensure free flow from the gray to black tank.
Yes, all tanks are beneath the floor so nothing will backup too far. And the gray tank will be filled from the top, and the start of the overflow into black will be beneath the inlet. I guess i can include another overflow on the gray tank to be safe.

When you talk about the ensuring flow from gray to black, ar eyou talking about debris blocking in the gray?
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Old 01-12-2022, 04:51 PM   #6
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When you talk about the ensuring flow from gray to black, ar eyou talking about debris blocking in the gray?
NO. I was referring to making sure you don't run the overflow hose UP then down thus preventing overflow from freely draining to the black tank.
Another thing to consider is filtering some of your gray and then misting that or dripping it into an evaporator plate attached to the hot exhaust while driving.
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Old 01-13-2022, 01:45 AM   #7
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When Ronco Plastics was roto-molding all my tanks I had them spin-weld 3/4" FPT fittings into the grey and poo tanks specifically so I could pump excess grey water into the poo tank. The grey tank's 3/4" fitting is about an inch above its floor to prevent any solids from getting sucked into the pump, and the poo tank's 3/4" fitting is directly above its 3" dump outlet. I use a small Harbor Fright utility pump to push grey water through a check valve and then straight down onto where any encrustations may form next to the dump valve. I can also jet water from shore through the poo tank's same 3/4" fitting, again through a check valve to prevent any cross-contamination. I anticipate my 115-gallon grey tank filling up much sooner than my 65-gallon poo tank, hence the transfer pump. Besides, it's better to dump the poo tank when it's completely full to ensure a forceful flow of turds through the stinky slinky.

You may want to use a transfer pump like I've done instead of relying on levels to equalize by themselves. If you were parked on a non-flat space, would your system work? Also, how well would an AAV such as a Hepvo work for water, especially water that may have some solids in it?

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Old 01-13-2022, 12:36 PM   #8
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If you were parked on a non-flat space, would your system work?
Or driving around with partially filled tanks? Could probably get most of the grey contents down into the black pretty easy. Maybe a valve in the transfer line for that case?
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Old 01-13-2022, 06:10 PM   #9
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" Another thing to consider is filtering some of your gray and then misting that or dripping it into an evaporator plate attached to the hot exhaust while driving. " <-- Not gonna lie, that sounds needless, complicated, and appalling.
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Old 01-13-2022, 06:46 PM   #10
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" Another thing to consider is filtering some of your gray and then misting that or dripping it into an evaporator plate attached to the hot exhaust while driving. " <-- Not gonna lie, that sounds needless, complicated, and appalling.
Appalling? Why so? In many states it's totally legal to dump gray right on the ground. In the 80's they still built slide in campers that didn't even have a gray tank even though they had bathrooms with showers.
FILTERING and then evaporating is an acceptable method and many municipalities utilize evaporation as a means by which to reduce volume not to mention industrial processes including nuclear power plant cooling towers.

Our build will be filtering water from the gray tank to reclaim it for showers, the washing machine, toilet flushing, washing the solar panels and the rig, etc. After real world in used testing, some of it may even be put into the potable water filtration system.
It's called recycling and it's something they do with ALL FLUIDS on the ISS......we'll just be using gray water.
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Old 01-13-2022, 08:12 PM   #11
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Because dribbling gray water onto the exhaust would aerosolize most of it...

...to be breathed later.


I'd rather is was dumped on the ground.
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Old 01-14-2022, 12:01 AM   #12
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...to be breathed later.


I'd rather is was dumped on the ground.

FILTERED would be the key here.
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Old 01-14-2022, 11:49 AM   #13
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That would be where the uselessly complicated part...

...comes in.


Filtering grey water to remove particulates and bacteria means you have a filter you have to backwash a lot. Why bother ?!
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Old 01-14-2022, 01:10 PM   #14
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If the water contains _anything_ other than soapy shower water- any food / drink particulates, its not gray water.. its black water, not meant to be dumped.. One of the regrets I intend to correct when things warm up is not installing a galley tank- which is black water from the kitchen sink.



Our "gray" tank (shower, kitchen/bathroom sink) is far nastier than our black tank (toilet only).
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Old 01-14-2022, 08:54 PM   #15
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There's a really good reason for reclamation if you're the type that likes staying off the grid as long as possible. And while some (many) may have mental predispositions to go "eeeew", it's nothing new. Think about the ISS....you think they dump their gray and black water? They reclaim as much as possible. Water is heavy and they do have to haul water up but a whole lot less than if everything consumed was dumped over when it became waste.
The military has reverse osmosis (RO) systems capable of producing pure water from ANY source. YES ANY SOURCE. So while they look for the best, cleanest, source, even a septic tank can be used to provide fresh water for drinking, hygiene, etc.

While you, and others, may consider kitchen sink water to be black water, the generally accepted definition is that black water is from the toilet and that showers, baths, sinks, etc. are gray. These are the definitions used in the RV industry, city planning offices, and legislative bodies. An argument COULD be made that bath and shower water can contain trace fecal matter due to the FACT that most people do wash that region and many do indeed urinate in the shower. So tou can fecal matter find its way into the washing water. But, the generally accepted definitions still apply.

Kitchen sink water is NOT black water by definition.
HOWEVER, our system will only be reclaiming water from the shower and washing machine as our intent is ONLY to extend, our 200 gallon supply to last as long as our food supplies with showers and the washing machine being major users of water.
After the system is built and operational, I will have it tested and we may plump reclaimed water back to the fresh tanks if it is sufficiently pure.
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Old 01-15-2022, 03:17 AM   #16
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Originally Posted by kazetsukai View Post
If the water contains _anything_ other than soapy shower water- any food / drink particulates, its not gray water.. its black water, not meant to be dumped.. One of the regrets I intend to correct when things warm up is not installing a galley tank- which is black water from the kitchen sink.

Our "gray" tank (shower, kitchen/bathroom sink) is far nastier than our black tank (toilet only).
In my experience 20+ yrs as a service plumber, by far some of the smelliest drains are the kitchen sink line.

The only potential issue I see with this setup is open path for bacteria from the black tank getting into the gray tank. I would suggest treating both tanks with a drain enzyme like "Bio Ross". There are other similar products, but I know this one works very well to all but eliminate smell and reduces any organic solids.
Good luck to you.
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Old 01-15-2022, 03:20 AM   #17
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Amzn link to bio ross product.
https://www.amazon.com/Bio-Ross-Bio-.../dp/B00LL5ZNE6
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Old 01-15-2022, 08:44 PM   #18
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Good point on having bacteria follow the path of least resistance from black to gray tanks MM.

Hopefully the OP has, or will, take account for that potential biohazard...?
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Old 01-16-2022, 01:04 PM   #19
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Good point on having bacteria follow the path of least resistance from black to gray tanks MM.

Hopefully the OP has, or will, take account for that potential biohazard...?
I guess a valve will be good, but the linked plumbing w valve would be no more/less linked from a bacteria standpoint than anyone that was a T-ed of dump valve (aka 1 dump valve for 2 tanks)... Right?
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Old 01-16-2022, 04:27 PM   #20
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While you, and others, may consider kitchen sink water to be black water, the generally accepted definition is that black water is from the toilet and that showers, baths, sinks, etc. are gray. These are the definitions used in the RV industry, city planning offices, and legislative bodies.
This is a very common myth, constantly cited by people dumping their nasty "gray" water on the ground and ruining good campsites. Yes, the RV industry uses the term Gray to refer to anything non-toilety, but every state I've looked into explicitly defines kitchen sink water as "black" and prohibits open dumping. My hope is to someday have enough time to track down links for each states regulations on this subject, but it kinda seems pointless. Anyone who has dumped a tank full of kitchen sink water knows how nasty it is. If those people somehow feel good spewing that nastiness for the next person to deal with, then I don't think illegality will convince them otherwise. For anyone considering dumping anything but clean rinse water, just... don't. Please.

Sorry OP, rant over.
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