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Author Topic: Do I really need a black water tank?  (Read 2858 times)
Jeremy
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« on: December 05, 2006, 02:28:08 AM »

There was a discussion on here some time ago about domestic vs RV toilets. I know many will disagree with me, but I have decided to go with a domestic type toilet in my bus.

I had assumed that I would need to mount the toilet directly above a black water tank, and fit a pump / macerator to the outlet of that tank so it could be pumped out. Having looked into things a bit more closely, I now realise that by spending slightly more money I could instead get a macerator unit that fits directly behind the toilet. The advantage of this type of macerator is that they incorporate a pump that sends the effulent down a narrow (1.5" or 1") hose - so the toilet can be fitted anywhere, and the position of the black water tank is no longer a constraint on the interior layout of the bus. You can also buy toilets that have the macerator and pump built into them, and these also have the advantage of not having a cistern - so they actually look exactly like high-end RV units. These toilets flush themselves by being connected directly to a water supply, although I haven't yet been able to determine how much water they use each flush (a modern dometic toilet with a cistern uses 3 litres, which is acceptable).

Getting back to the point of the post - if I use a macerating unit in or behind the toilet, do I still need a black water tank? They are designed for installation (in houses) where there isn't a sewage drain available - the effulent instead goes down the regular waste pipes from the sink, shower etc. In theory therefore the toilet outlet in my bus could be plumbed straight into the grey water tank and dispense with the black water tank altogether. Anyone got any views on this? Naturally I am worried that there would be odours coming up from the grey water tank through the sink and shower plug holes - but then, the standard u-bend fittings beneath sinks etc are supposed to stop any odours coming up from the drains aren't they?

If anyone has any thoughts or experience on this I would be interested. Avoiding having to fit a third water tank would be a major benefit, but then again I don't really want to be the guinea pig who tries a new idea and ends up with a smelly coach

Thanks

Jeremy
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« Reply #1 on: December 05, 2006, 03:30:05 AM »

Hello Jeremy,

Now that I've been using my coach for a year and a half, I have had the pleasure of dumping my tanks many times...

My black water tank can get a bit ugly at times. I'm glad that I'm able to flush out the dump hose and fittings with gray water afterwards.

Another advantage of seperate gray/black is that you can [if need to] releve the gray tank without finding a dumpstation.

It seems that my 40 gal. black tank almost never fills up. and my 105 gal. gray is always ready to dump... Therefore, inableing me to

releve the gray tank without leaving a smelly mess. I also use a macerator pump, but only at the tank outlets when too far from dump, or when gravity

is against me. My Sealand Magnum Opus [without vaccu-flush] does a very good job in conserving water too.

You do what works for you.

Good Luck
Nick-



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« Reply #2 on: December 05, 2006, 05:14:20 AM »

Ok, it's clear from you post that you may not fully understand the terminology. So...

If you put waste from toilet into a tank, it is, by definition, a black water tank. Does not matter whether it was dropped straight in from the toilet, came down a sloping pipe, or was pumped in by a macerator pump. If you put human waste in it, it's a black tank.

A grey water tank contains only water from the sinks and shower/tub. No human waste.

So your question is not whether you need a black tank (because the answer is if you intend on storing sewage water, then you have to have a black tank), but more appropriately, can you use a single tank that combines the black and grey water? And the answer is a definite yes.

In my opinion, there is really no good reason to have a split system, unless it eases the layout of the floorplan or bays.

Many will disagree with this, and they all have valid points which work well for their needs, but the fact remains, that in probably 99.99% of the time, they, and everyone else, collects every drop that goes down the drain in a tank of some sort, and it is eventually dumped into a sanitary sewer.

How you get it into the tank is up to you. If you find that the macerator connected behind a household toilet will work best for your needs, go for it. They're cheaper than an RV toilet, and some of them use not much more water than the RV toilet. The biggest reason for not using a household toilet is water conservation, but if that's not a high priority for your needs, do it your way and enjoy. Keep in mind that if you use a household toilet, you'll have more water to push the solids, so would not necessarily have to mount the toilet directly above the tank, but rather, could use a sloping line from the toilet to the tank, within reason.

« Last Edit: December 05, 2006, 07:14:19 AM by gumpy » Logged

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« Reply #3 on: December 05, 2006, 05:22:40 AM »

And, before everyone jumps on the thread talking about how you can't dump on the ground, you should view this video that aired on local TV last night.

http://www.kare11.com/news/investigative/extras/extras_article.aspx?storyid=139463
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« Reply #4 on: December 05, 2006, 06:32:48 AM »

Hi Gumpy

Thanks for the answer - exactly what I wanted to hear. I take your point about the grey tank becoming the black tank as well. It'll certainly reduce the work and expense if I only have to fit two tanks, so I'm glad you think 'my idea' will work (for all I know it could be common practice on new RVs now).

Re. the dumping of sewage - I heard a history documentary just a couple of weeks ago about the English vicar who invented the 'earth closet' in the seventeeth (I think) century, which played a major part in stopping the frequent Cholera epidemics of the day. Apparently, long after the invention of 'water-based' sewage systems, earth closets remained popular and are still thought by many to actually be a more satisfactory sytem, as they actually render the sewage harmless rather than simply moving it about as water does.

Jeremy

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« Reply #5 on: December 05, 2006, 06:50:43 AM »

In the early days of RV'ing, it was common practice to dump gray water tanks along side the road, or anywhere it was convenient. Sometime in the late 70's or early 80's Oregon passed a law making that illegal and requiring a cap on the gray water tank. Many of the early RV's did not even have a gray water tank. It just dumped directly on the ground anytime a sink or shower was used.
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« Reply #6 on: December 05, 2006, 07:15:07 AM »

If done 'properly', I doubt anyone would really care if you dumped your tanks on the ground. The problem comes when  people are inconsiderate of others. I shouldn't have to walk thru or around your waste, & vice-versa.

Concerning the macerator, sure they work, but that is another thing to maintain & work on. I plan on having one, but it will connect to the main dump outlet if I need it. otherwise, it will be stored & unused. Also, If the toilet mounted macerator quits working, you are likely to really, really need it to work just one more time  Grin   Also when it isn't working, neither is your tiolet  Cry  Angry

Contrary to what some will tell you, the toilet does not have to be directly over the waste tank. It is easier to make work that way & uses less water, but there are loads of RV's out there that work just fine with the toilet not over the waste tank. For those systems to work, the waste piping causes minimal restriction to the waste travel. They also require more water, but you are already talking amout 3 liters per flush. Do the math & that will tell you the size tank vs how many flushes between dumps. See why less water per flush can be a good thing?

In the camper my parents used, the toilet was directly over the waste tank & you could usually flush the heaviest loads with less than 1/2 liter of water.

There are problems that can arise in a black tank that gets very little water added (curing the constipated tank is not something I EVER want to do!  Shocked

I'm planning on a combined tank with a simple gravity flush, minimal water use toilet, but that is just my way. (I know the problems with this type, but they aren't show stoppers & are usually predictable.
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« Reply #7 on: December 05, 2006, 07:29:04 AM »

I am in the process of doing the plumping and I am going with one combined tank for black and gray.  I think it will suit our needs just fine.  I am regret it - if I do, I can redo some of the lines to include at gray at a later time.  I am leaving the room for that option.

Danny
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« Reply #8 on: December 05, 2006, 09:00:02 AM »

I vote for just one tank..Our 4th conversion have been living in it since 2000. Just one tank 180gal dump every week and a half if some where with hook ups..If at car show or trade show can conserve and go three weeks if we have to...Use 1 1/2 gal home style throne..Greatest thing about using home style vs rv is NO odor...We use a digester about twice a year to make sure the tank is clean ( only when we are doing short programs that put us in three or four places within a 2 week period with lots of driving to mix the tank up good..) other than that no chemicals needed and no smells..gg04
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« Reply #9 on: December 05, 2006, 04:57:17 PM »

I believe in the two tank system.  I have a 45 gal black and 85 gal gray.  If the gray gets full, can descretely dump without stinking the neighbors out.  The 45 gal will last at least a week.

As to the tank being directly under, my black tank is mount fore and aft on centerline with the toilet on the right side of the bus connected with about a 3ft line going sideways to the tank.  Works everytime, although with a little more water than a direct dumper.

Jeremy-  I would suggest two tank system, and especially the RV type toilet.  If you have a regular toilet and the syphon seal gets broken from vehicle movement, you'll have a direct path to the tank-meaning serious smell.  I have a Sealand 510 and really like it.  It looks great and works well.  And you can't get any more simple than gravity.  Good Luck, TomC
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« Reply #10 on: December 05, 2006, 05:26:06 PM »

 Great post Gumpy, I've known this but never seen it in print. Anyway I use the one tank system works well for me. The line from the toilet is offset about 6 inches with no problem. Also when ordering tanks I had an extra eaisely accessable 3 inch opening put in the top of tank for rinseing, cleanout ect. I also mounted a macerator pump to the tank so I can dump either way.
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« Reply #11 on: December 05, 2006, 06:40:43 PM »

I also vote for two tanks...and that's from fulltiming experience.  I've been parked for a month.  I can dump gray without a problem but I have to take the bus 30 miles to dump black.  I can go a week on 70 gallons of grey and over a month on 50 gallons of black.  In fact, I just dumped black yesterday and the last time I dumped was about a month and a half ago, just after Timmonsville.  If I had a combined tank, I'd have to travel to the dump station at least once a week.  I have a Sealand 510 toilet.  If I had a household toilet, the tanks would fill up 4 times as fast.

Ross
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« Reply #12 on: December 05, 2006, 07:59:23 PM »

Jeremy,   All good points except comments are all from people in US or Canada,  I think you need to start with researching what dump facilities are generally available in th UK and what is acceptable at those facilities.

It's more than 30 years since I was camping in the UK and but that time you could list all dump sites on the back of a stamp.

Dave,  originally Hinckley Leics.
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« Reply #13 on: December 05, 2006, 08:23:39 PM »

My coach has one black/gray tank.   It's 110 gallons.  Takes a lot to fill it up.  Seems to work for me.  Of course I'm new to this and may change my mind in a year.... Undecided

Bill Williamson
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« Reply #14 on: December 06, 2006, 02:40:16 AM »

Thanks to everyone for all the useful replies. It's clear that there are various ways of configuring the system, all of which will work equally well but have their own particular advantages and disadvantages. Dave970's comments about dumping stations for black tanks is well made - to be honest I don't even know what one looks like. No doubt they exist on campsites here, but I'm not intending to spend much time on campsites with my bus. Also, the idea of having a black-only tank, and carrying the contents around for weeks doesn't appeal. Although I take the point about the advantage of being able to discretely dump grey-only tanks on the ground, I think I will end up with one combined grey/black tank and dumping properly directly into the sewage system each time.

Last night I had another look at the bus to think about the positions of tanks and the toilet - since my bus is mid-engineed, the side baggage bays are relatively small, as they don't go right the way across. I also want to keep the baggage bays empty for, well, baggage. Which all means that the water tanks really have to be mounted centrally, above the propshaft between the gearbox and the back axle. There is a very big open space there, and the weight of the tanks will be ideally positioned, but actually getting the tanks in there will be a tight squeeze. I could always put the tanks in the coach's  huge rear boot (trunk), but the weight positioning would be all wrong, and there is also no chassis back there to support the weight of the tanks. So they need to go centrally - but there is no way at all I can have the toilet located right in the middle of the bus - in fact, where I really want to mount the toilet is directly above one of the rear wheelarches. So I suspect a 'gravity drop' into the tank is out of the question; I still need to do some more research, but it is looking like a macerating toilet is the answer at the moment.

Thanks again for the replies

Jeremy
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