Gray/Black tanks

Flight102C3 · April 20, 2011, 05:21:31 AM

HI! What are the pros/cons of combining the two tanks?? thanks for now!

robertglines1 · April 20, 2011, 08:25:06 AM

some places let you discharge gray water. two tank system =dump black first& flush with gray. I've done it both ways. I'm usually on full hook-ups (life style) Bob

Sean · April 20, 2011, 10:03:11 AM

Tons written about this already -- check the archives.

In brief:

A combined tank automatically compensates for differential usage. IOTW, a single large tank will always let you go longer than two smaller tanks whose combined volume is the same as the larger one, because with the smaller tanks, one invariably will fill before the other, forcing you to go dump even though there may be space left in the other tank.

Some hard-core boondockers will also argue that if you are in a place where you can let shower water run out onto the ground (rare, but they do exist), that a single large tank combined with a "diverter valve" for the shower drains lets you extend your boondocking time considerably, because the large tank is now only having to hold black waste and kitchen waste.

On the flip side, if you have a combined tank and it fills up, you will have raw sewage backing up into your shower (yuck). With separate tanks, if they fill up, you will only have gray water (still no picnic) backing up into the shower.

Also, if your fixture traps empty, as they will do occasionally when driving down the road, with a combined tank you will get sewer gas coming into the coach. Again, the gas in the gray tank is less of a problem.

Another benefit of separate tanks is that you can dump your gray tank after you are done dumping the black tank, so the sewer hose gets rinsed of black water before you have to uncouple it. With a combined tank there will be some black water residue in the hose when you have to handle it. If you add an additional fullway valve downstream of the black and gray valves, you can even use the gray water to back-flush the black tank when you are dumping.

If you spend a lot of time in one place on full hookups, with separate tanks you can just leave the gray valve open, and you will only need to dump when the black fills. With combined tanks you'd need to keep the valve closed and dump more frequently. (Black valves should not be left open, to avoid an unpleasant build-up of solids in the tank.)

HTH,

-Sean
http://OurOdyssey.BlogSpot.com

Chaz · April 20, 2011, 10:25:06 AM

Good synopsis Sean.
There has been a lot written and that sums it up well.
As far as what works best....... that's a personal thing.
Chaz

TomC · April 20, 2011, 01:09:25 PM

I have 130gal fresh, 85gal gray, 45gal black. On the gray I have a curb side dump so that I can pull up by a street drain and empty it, or if I'm in a situation I can dump the gray on the ground. I'll always suggest the two tank system. On my truck I'm using a 210gal fresh, 115gal gray and 70gal black-why-cause I can. Good Luck, TomC

wal1809 · April 20, 2011, 03:41:31 PM

Here is a pic of the gray tank I put in not long ago. I intend to box it in for storage on top and to make it look a little better. Oh and by the way it is not vented

scanzel · April 21, 2011, 03:07:45 AM

Tom C. I would hope after making the comment about dumping gray water into a street drain you change your ways. Not only does it pollute the water, but many street drains go into local ponds and lakes. This can cause pollution to the fish and water fowl and cause increased growth of vegetation. Plus it is an offense if caught by locals or the DEP. Very stiff fines can be levied.

garhawk · April 21, 2011, 05:06:33 AM

How much pressure builds up in that unvented barrel before it refuses to accept any more grey?

TomC · April 21, 2011, 07:10:27 AM

Steve-then we'll have to tell animals to quit pooping, gardners not to fertilize lawns, people not to wash cars (soapy water from washing a car is far more toxic then the diluted soapy water from your gray water), cars and trucks not to drop oil, gasoline, Diesel fuel that gets washed down the drain when it rains. Not trying to be mean-just making a point. Good Luck, TomC

wal1809 · April 21, 2011, 11:50:42 AM

Quote from: garhawk on April 21, 2011, 05:06:33 AM
How much pressure builds up in that unvented barrel before it refuses to accept any more grey?

Never had any trouble with it. I usually just leave the drain hose valve open anyway. I have had it half way full without draining but it gave me no issues.

Flight102C3 · April 25, 2011, 08:22:37 PM

Thanks for the information. I will search the topic. Thanks again for the help!! Flight 103

luvrbus · April 25, 2011, 08:43:57 PM

Steve, find out where TomC dumps his gray water in a storm inlet and I have a 800 number for EPA and we can make a few bucks here man lol if he get's caught those guys will eat him alive.
They caught my water truck driver dumping clean water into a inlet in Tulsa and had a run away till we proved it was clean water to wash the inlets to get a final inspection on the job

good luck

happycamperbrat · April 25, 2011, 08:53:20 PM

Wow! They have tightened up in the last 10 years! One time I was parked on a dirt lot near a park and while my kids were playing I was washing dishes. I had the gray open and it just so happened a police officer came buy and spotted it. He came up and asked what it was and I told him "dish water", he then put his finger in it and smelled it

And then went on his way..... that was here in Cally too where they are really tough!

Dave5Cs · April 25, 2011, 10:43:40 PM

Now in California they have a fish decal and it says don't pollute my home at every drain in parking lots and when I used to build new homes and we were breaking ground, we had to put hay-rolls around all drains to catch anything that might go down them. If a Tile guy drained his grout water down them or a painter washed out his brush or rollers in them they would be fined and hazmate sent out and they would be charged with the clean up bill. It is getting a little out of control.

happycamperbrat · April 25, 2011, 11:09:22 PM

My brother has had run ins like that. He used to work in Trona California for a large mining company (it was actually on Dirty Jobs once). Sometimes they would need things hauled in and some of the stuff they needed would be contaminated with stuff they didnt need. But because the stuff they didnt need was the very same minerals found on site they thought they could dump it and it would not be polluting. WRONG! The EPA said although it is the same minerals as found here naturally, these particular minerals didnt come from here so they cant stay!