Size of Black versus Grey Tank

[Oonrahnjay]

Is you were building tanks to match a 115-gallon fresh tank, what size would you make the black and what size would you make the grey tank? 

[Len Silva]

I think 60/40 or even 70/30 is about right.  I wouldn't necessarily limit the waste tanks to the size of the water tank.  There may be times (like in state parks) where you have water hookups but not sewer.  The larger the better.

[Melbo]

I did the approx 70 30 deal the first time (I have 150 fresh and I had 110 gray) and I think 20 to 25 gallons of black is plenty for two people.

If you have kids you may want something larger but I have found that with a 25 gallon tank and two adults full time in the bus (plus the occasional friend or two) we can go for a week and approach 2/3 full.

HTH

YMMV

Melbo

[Jriddle]

I made one gray/black tank the same size as the fresh tank. I did plumb a gray bypass to let grey go to the sewer when hooked up. I have been using this bus for two years now and don't see the need for gray tank. My tanks are 108 gal.


My Way
John

[Tevo]

I made one gray/black tank the same size as the fresh tank. I did plumb a gray bypass to let grey go to the sewer when hooked up. I have been using this bus for two years now and don't see the need for gray tank. My tanks are 108 gal.


My Way
John

Lived in my travel trailer for a year and now am in the bus and am redesigning the plumbing system to mesh better with how I live. I've found the same thing you did, as I don't see the need for two tanks. I've never dumped grey water on the ground and don't plan to, and  in my experience the notion that the grey is going to clean out your hose when dumping is really overrated. If you figure your black water is maybe 20-30% of your grey, max, you really dilute the black by combining them and have less problems with tank sludge and such.

Of course, I know others have lots of opinions on this, but I really like the simplicity of one tank, and the benefits that come with it. To each their own of course.

[white-eagle]

dumping grey is not very bad.  dumping black is.  if it were my yard, and you wanted to dump sink water, no problem.  dump the toilet, no way.
we have separate grey and black.  yes, the grey is not clean fresh water and stinks, but not near like black. 
if you plan to boondock, or stay somewhere without ready access to a dump, i'd suggest separate tanks, with an easy way to trickle the grey out, with permission in the right places.

i do agree with Melbo that a week can fill a 20 gal black tank.  some of us are more full of it than others.  We seem to have issues running 3 weeks on 80 gal. but the grey sometimes overflows into the black if i don't catch it in time.

it really depends on how you plan to boondock or camp without a dump.  do a lot, get a bigger black tank.

we're now where i need the black to last at least 3 wks.  glad i don't have a 30 gal black tank.

[Jriddle]

I did plumb a gray bypass to let grey go to the sewer when hooked up.

This would allow to dump on the ground as White-eagle has suggested.


John

[mugsytrpt]

I would have to agree.  I like them seperate.  I understand only one tank and if you are going mostly pole to pole or should I say sewer to sewer one tank will be great.

James

[Oonrahnjay]

I did the approx 70 30 deal the first time (I have 150 fresh and I had 110 gray) and I think 20 to 25 gallons of black is plenty for two people.

If you have kids you may want something larger but I have found that with a 25 gallon tank and two adults full time in the bus (plus the occasional friend or two) we can go for a week and approach 2/3 full. 

Thanks, I forgot to mention that I have an "Atlantis" low-water use mascerator toilet.  Also, The Management is still working (to help pay for my toy) so I'll probably be in the bus by myself often (our plan is for me to drive someplace, she'll fly to meet me, we'll vacation for a week or so, then she'll fly home but I'll drive back).  Also, she's more of a homebody than I am.

[TomC]

I have 130gal fresh, 85gal gray, 45gal black.  I can fill the gray first-but as mentioned, can dump it if the situation is right.
On my truck, have 2-98gal fresh, 145gal gray, 60gal black-because I can.  Good Luck, TomC

[Oonrahnjay]

(snip)  don't see the need for gray tank.

Yeah, I think I'd prefer a single tank but my bus isn't configured so that there is room for one.  Have to split to fit in the frame rails.  Thanks.

[AndyG]

but the grey sometimes overflows into the black if i don't catch it in time.

How does this work?  Are your tanks plumbed to allow overflow from the grey to go into the black.  What keeps the black from running into the grey?

[Iceni John]

but the grey sometimes overflows into the black if i don't catch it in time.

How does this work?  Are your tanks plumbed to allow overflow from the grey to go into the black.  What keeps the black from running into the grey?

Either have the grey higher than the black, to prevent siphoning (having black "water" coming back up the sink or shower drains is Not Good), or do as I will, have a small transfer pump to move grey when needed into the black.   The pump's outlet will be high in the black tank's vent, again to prevent any chance of contact with the pee and poo.   This is also where check valves can be useful (until they clog up and need to be cleaned out . . .)

John

[AndyG]

Thanks John.  My rig has equal sized tanks.  We have figured out that the black tank does not need to be nearly as big as the grey.  I did have trouble this summer with the grey filling up and there was still lots of capacity in the black tank.  I guess I could use the campground shower but that degeats the purpose of having a self-contained RV.