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Old 06-14-2006, 11:07 AM   #1
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1994 30' Excella
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Milwaukee , Wisconsin
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Gray Water Diverted Into Black Water Tank

I am the volunteer host at a state park for the month of June. There is an electric hook up but no sewer. After two weeks my gray water tank has needed to be pumped out twice but my black tank gauge has yet to budge off of E. We are located right across from the bathrooms so it is easy to walk to the facility reserving Chummy's toilet for night time and emergencies. However, it always seems that I fill up my gray tank several times before my black tank even begins to need emptying. Question is, what would be the drawbacks to having an overflow of gray water into the black water tank? I seem to recall that AS did this at one time but it was not a success although can not remember why.

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Old 06-14-2006, 11:23 AM   #2
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The way the sewer lines are set up in our '64 GT you can do this, with mixed results.

The sewer line is a "Y" shape with the grey water normally by-passing the black tank completely and we don't have a grey tank. To store grey in the black tank, you would put the "termination cap" on the exit portion of the "Y" and open the valve to the black tank. The grey will back up to the black tank. This works on our model because the black tank is below the floor, some models are not like the '65 Caravel amog others, which are above the floor so it would back-up to the shower (yuck!).

The only problem with this whole thing is when you go to empty the tank. You close the valve to capture the contents, but there is a small amount trapped between the term cap and the valve. So when you remove the term cap, some spills out (double yuck!!) Yes, it's diluted...but I still don't want any on me or at my campsite!

You may want to look into a blue belly to handle the extra grey in between black dumps. The blue belly can be emptied of the grey into the restroom drain...or saved until you go to the dump station, effectively enlarging your capacity.

If there were a way to capture your grey overflow and fill it to the top of the black tank, rather than from the bottom in my scenario, the concept would work a lot better.


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Old 06-14-2006, 11:45 AM   #3
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hi ck and others....

several issues, i'll list just a few quickly.....

-cross contamination.....while there are bacteria in grey water, there is no where near the concentration as in the should black seep back into the grey....eck! while the tanks vent, gases could back up via the sink traps into the coach....i have experienced this first hand....nasty!

-surface dumping of grey water....if the connecting tanks were to cross contaminate.....dumping grey water on the ground (still ok many places) would take on a new meaning....

-keeping the black tank healthy......need lots of good bacteria in the black tank to digest fats, carbs, proteins, cellulose and so on...grey water usually has soap, detergent, cleaners, household chemicals and raw food bits. these things would kill the good digestive bacteria in the black tank.....SO THE BLACK TANK WOULD REALLY STINK!......

there are other issues like filling the black tank so fast during a what if you need to poo and flush?

best to get a blue tote with 4 wheels and a handle....24-28 gallon size is about the biggest one can pull around easily.....

and remember the black tank wisdom that boaters follow.....

'put nothing in the black tank you haven't eaten first'....

all of the true things that i am about to tell you are shameless lies. l.b.j.

we are here on earth to fart around. don't let anybody tell you any different. k.v.
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Old 06-14-2006, 11:45 AM   #4
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another way

hi- I don't know how hard it would be for you to re-route some of the waste plumbing, installing a diverter valve that would allow you to, in tough situations, run the greywater into the top of the blacktank via the vent pipe- I did this when I gutted and re-modeled my rig, easy to do then. Just a thought, I'm sure there other solutions out there. -tim
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Old 06-14-2006, 04:38 PM   #5
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Kent, I ran the drain from our kitchen sink into our black tank, with good results. Doing this in this manner keeps the black bacteria from gettin ginto the grey tank, keeps the contents of the black tank diluted enough to flow freely our the slinky, and the soap in the dish water seems to help keep the inside of the black tank clean.
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Old 06-14-2006, 06:38 PM   #6
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Last summer we rented a four winds class c in alaska. The third day out we found the black tank full, with little in the gray tank. Seems that they ran the bathroom basin and kitchen sink into the black tank. The gray tank only serviced the shower that was on the other side of the unit. Fortunately we were able to dump every three days.

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