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Old 03-23-2020, 10:36 AM   #1
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Urine, Grey Tanks, and Pumping Out

Well, I'm a big dummy. I've never owned an RV, but I did use to live on a sailboat, so my only experience with grey/black tanks was with marine pump out systems. My boat had a particularly difficult method to pump out, and rarely worked, and was a messy ordeal.



So I just assumed it was the same way with RV/Skoolie pump out stations. Because of my awful experience with my marine tanks, I wanted to avoid this whole situation on my Skoolie. So my design calls for a composting head, with urine being directed into the grey tank along with the sink drain.


Since we primarily use Argo for boondocking, I figured just dumping the grey tank prior to leaving whatever logging road we were on would be no different than taking a piss on the ground or dumping dishwater behind a tree (biodegradable soap and all).



However, thanks to some public shaming on this forum directed at me and my "genius" plan, I discovered there was something I wasn't considering: keeping urine and dishwater in a tank for days at a time allows it to ripen, and then dumping ten, twenty, thirty gallons of this ripe liquid in one spot is not the same as just taking a piss behind a tree. And it's also disrespectful to the intent of Tahoe National Park (open for everyone, pack in/pack out, etc...).



On top of that, I now realize that using an RV dump station is nowhere near the same as it worked on my sailboat. It's stupendously easy and simple. However, my tanks are already installed so I can't really change or add anything new. But maybe you could critique my new method and tell me what I'm missing:



The drain on my grey tank is a 3/4 ball valve (https://www.amazon.com/gp/product/B0764NBD7L/), so can I just attach a 3/4 hose to this drain, put the other end in the dump receptacle, then open the drain valve? Then also turn the sink to flush out any remaining liquid? This is just a grey tank, so there won't be any solids bigger than the holes in the sink drain, so I think the hose size will be fine.


Any thoughts?
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Old 03-23-2020, 11:01 AM   #2
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Originally Posted by TheArgobus View Post
The drain on my grey tank is a 3/4 ball valve (https://www.amazon.com/gp/product/B0764NBD7L/), so can I just attach a 3/4 hose to this drain, put the other end in the dump receptacle, then open the drain valve? Then also turn the sink to flush out any remaining liquid? This is just a grey tank, so there won't be any solids bigger than the holes in the sink drain, so I think the hose size will be fine.

Any thoughts?

Yeah, that stuff gets pretty nasty smelling as it ferments. RV dump stations are dead simple. If you're able to, I highly recommend just using a standard RV valve and dump hose. It's so quick and easy. At first I tried a 1 1/2" ball valve with a flathose and that didn't work at all...the hose stayed flat. I changed over to a normal 3" valve after that debacle. I know they make regular hose fitting adapters for RV tanks, and I think people use these to trickle out the gray water. This is just a hunch, but I worry it might take quite a while to empty a full tank with a 3/4" hose and people lined up at the dump station tend to get ornery with non-standard practices (as I learned the hard way).
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Old 03-23-2020, 11:09 AM   #3
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Yes do avoid the flat hose, we tried it to and it stayed flat as well. I have a garden hose for the grey and a 2" hose with a quick coupler for the black, and have found this works well for me. Both tanks are 50 gallons each
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Old 03-23-2020, 03:59 PM   #4
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Originally Posted by TheArgobus View Post
Well, I'm a big dummy. I've never owned an RV, but I did use to live on a sailboat, so my only experience with grey/black tanks was with marine pump out systems. My boat had a particularly difficult method to pump out, and rarely worked, and was a messy ordeal.

SNIP...

Any thoughts?


Thanks for rethinking your plan...

Sailboat probably had to pump everything uphill to get it off the boat...

Gravity can be your friend!

As said 3/4" is gonna take longer than you like, and I wouldn't take any risk on something going down that can then clog it...
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Old 03-23-2020, 08:45 PM   #5
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I think I was one of those who said something in that thread and I felt bad about it. But I'm glad you're rethinking your plan.
I still haven't thought through all my options but I'm going to have to make a decision soon.
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Old 03-24-2020, 05:09 AM   #6
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I have experience with boat pump outs and typical RV dumping (3" gravity hose - not to be confused with RV macerator pump outs). As you say, they are very different things. With so many RV's working very well, I'm not sure why that approach would be altered. It would just be creating problems that have already been solved.

So, I would suggest you stick to the standard RV approach. There are many existing accessories/parts (valves, hoses, etc.) that are all proven to work.
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Old 03-24-2020, 05:42 AM   #7
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I have no suggestions other than follow that which has already been suggested ... the RV dump stations are set up for RV style connections. Best to stick with that which is proven.
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Old 03-31-2020, 03:27 PM   #8
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A LITTLE UNDERSTANDING PLEASE! I think this post is on the right track, it just needs a little practical application. Get a high pressure pump and mount a sprinkler head on your back bumper. Grab one of those California signs "this area is watered with reclaimed water" your home free. It should take care of any tailgaters as well
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Old 04-01-2020, 11:21 AM   #9
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Originally Posted by WHATPARTHURTS View Post
A LITTLE UNDERSTANDING PLEASE! I think this post is on the right track, it just needs a little practical application. Get a high pressure pump and mount a sprinkler head on your back bumper. Grab one of those California signs "this area is watered with reclaimed water" your home free. It should take care of any tailgaters as well

Well, that settles it! I'm going with this plan!
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Old 04-04-2020, 03:18 PM   #10
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Thanks for being open to reconsidering your position on greywater disposal. Your original plan was really beyond the pale.
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Old 04-04-2020, 05:16 PM   #11
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As others have suggested I also suggest you get a bigger hose like the standard rv hose. If not I’d be concerned with clogs in a small 3/4” hose. Even if small chunks fit down the sink drain they can expand in water and build up/combine to clog the small hole. If you really don’t want to change out that 3/4” I’d at least put on one of those fine sink drain screens to catch everything and get a real commercial size 3/4” hose. (The standard garden hoses are usually 1/2” or 5/8”)
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Old 04-04-2020, 08:12 PM   #12
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I ran my urine diverter hose to A plastic Jerry can I have mounted below the composting toilet. I can just carry the Jerry can to empty it in a toilet or urinal of needed.

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Old 04-04-2020, 09:30 PM   #13
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I agree with everyone who says you'll probably want a bigger outlet than 3/4". And if you go with standard RV size and fittings it makes it easy to replace your hose or borrow another length from someone if you ever need to do so.



As far as the conversation about outlet diameter, maybe I can add some food for thought if anyone is interested. I don't mean to beat up the OP who asked a good question and I hope it doesn't come across that way, but this is something I know a little about and maybe it's a good time to point out what might not be "common sense" to some skoolie builders.



There's often a difference between "nominal" size and actual internal diameter for pipes and hoses. I don't know offhand if RV plumbing and garden hoses typically use internal diameter or outside diameter or something else for their nominal size naming conventions. If it's something that will matter for your application, it's worth finding out for sure what that nominal size is actually referring to, and how it compares to actual dimensions. With that said, since I don't know specifically in this instance, I'll assume for illustration purposes that the nominal sizes are the measured internal diameters.



A common size for RV tank outlets is 3". The cross-sectional area of a 3" outlet is (PI/4) X (diameter squared), or 7.1 square inches. The cross sectional area of the 3/4" outlet is 0.4 square inches. So, while 3/4" to 3" doesn't intuitively seem like that big a difference, the 3/4" pipe is only 6% of the flow area of the standard RV plumbing. 6%!



To make matters worse, you probably won't even get 6% of the flow, due to a characteristic generically called pumping losses. Basically, using the formula above, we can see that area increases or decreases faster than diameter when we change the diameter of our pipes. So therefore more of the fluid is in contact with the walls when it flows through the smaller pipe, significantly increasing "friction". Additionally, sharp angles, surface roughness, pressure, pipe length, and other common factors start to have a bigger impact too. The end result is that in this application you will probably see something like 1% to 3% flow rate from a 3/4" outlet hose, compared to the 3" option. Not (.75"/3") or 25% flow rate as one might mistakenly assume.



Somebody please feel free to check my math. I think I got it all close enough but maybe not. Regardless, my point is that there are good mathematical reasons behind all the suggestions that 3/4" might be disappointingly small. Even before a big piece of corn gets lodged in there and stops ALL flow. FWIW, I hope this helps someone in their decision making.
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Old 04-04-2020, 09:58 PM   #14
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You need to observe the state regulations when openly dumping gray water. In New Mexico, shower water or wash water may be dumped on the ground, however dish water or any water that may be conlaminated by food may not. Urine is considered sewage in New Mexico as well.
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Old 04-04-2020, 09:59 PM   #15
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I just cannot wrap my head around the lure of composting toilets! I've not had one yet in a home or RV build, maybe I'm missing something.....
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Old 04-04-2020, 10:22 PM   #16
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I just cannot wrap my head around the lure of composting toilets! I've not had one yet in a home or RV build, maybe I'm missing something.....
I am right there with you. I have grown up with RVs. The first one had no bathroom and seeing that my dad would seemingly never stop, us kids would have to use one of those toilet seats with a kitchen trash bag. I suppose that’s the closest we got to a composting toilet. I think the term “composting toilet” is a misnomer since no one keeps their poop long enough to compost. I’ll probably catch some crap for that.

I guess the good thing about a composting toilet is that you never have to look for a dump station.

And if you’re in some places you may have a hard time finding a dump station. I just looked at the Bay Area and they need some more stations. So if you’re “camping” in the Bay Area you might benefit from a composting toilet, though a cassette toilet might be more appropriate
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Old 04-04-2020, 10:53 PM   #17
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The pluses of composting toilet:
Less water use
Easier to install in conversion
No black tank needed to buy or empty

Regardless I still went with a Rv toilet and black tank.
Pluses:
Easier when in a Rv Park with full hookups
Easier for young kids
Not as gross (for me anyway). It’s probably easier to dump Rv tanks than to change out a compost toilet. Just possibly less convenient...
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Old 04-05-2020, 12:43 AM   #18
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I have lived full time with both. Eight + years.

There was no hesitation in picking a composting toilet over a conventional RV toilet & black tank for our bus.

The folks that introduced me to composting toilets actually did compost their waste. They were off grid self sufficient sorts.
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Old 04-05-2020, 03:00 AM   #19
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I have a year of full-time RVing experience in a higher-end RV with the conventional tanks and dump station operations (2 people, never ever boondocking for more than 1 night), and also a few seasons of using a composting toilet which I built myself using cheap non-purpose-built materials at an off-grid cabin (1 to 10 people, seasonal use in the northern US). Nothing about the RV tanks and dump stations really bothered me, but if it's me dealing with the waste products I'd prefer the composting toilet process any day. Once we got the composting system figured out, there was no smell, it was cheap to operate, less environmentally unfriendly, no concerns about tanks freezing, and easier to store the waste for longer if necessary. And as an added bonus the end product was a pretty good fertilizer. We never used it for food plants (for us, not worth the risk), but with appropriate precautions I think we easily could have. I have zero experience with the commercially-available composting toilets but I would hope for the prices I see they better be even more user-friendly than a homebrewed setup. However, I can't really see a way to compress that operation down to a size appropriate for a bus installation without losing most of the benefits.If you're going to throw the end result in a dumpster anyway then what's the point. If I was going to be doing short trips (2-3 weeks or less for 2-4 people), and regularly returning to somewhere I could maintain a proper compost pile, that would make the composting option a no-brainer. Since I expect to use my bus for full-timing, I think I'll probably end up going with something more like the typical RV tank setup just for the convenience. For where I've traveled, legitimate dump stations have been plentiful enough if you know where to look and/or are willing to pay for the use. I haven't RV'd in the Bay Area though, maybe that would change my mind.
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Old 04-05-2020, 05:34 AM   #20
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If you decide to go with tanks use the purpose-made fittings. As a space making strategy I was also going to add a 3/4” valve so I could draw off into a bucket and dump it into a drain somewhere, but then I found out they have a cap with a hose fitting that fits on the 3” drain opening. If you’re going to have a dedicated black tank, try to tie the grey and black tanks together just after the valves. This way when you empty the black tank, you can use the grey tank contents to rinse the drain hose.
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