#1&#2 holding tank simple ?

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visch1

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Joined
Apr 27, 2008
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Cape Cod, Ma
Yesterday while emptying my 2 tanks I started to wonder why have 2 tanks when it all goes to the same place where I dump. At most if not all places with septic systems it?s all into 1 tank then distributed into the leaching system. I?d expect the plumbing system would be simpler with a 1 tank system.  What simple answer this simple mind doesn?t understand?    :-[
 
I've wondered about this from time to time and concluded that it dates back to the time when it was acceptable to dispose of gray water most anywhere but never so with black waste. That's just my opinion and not backed by any industry source (I doubt if anybody would admit such a thing now).  And I suspect the two tank system remains because some (many?) people do sometimes take advantage of the separate gray to dump waste in a politically incorrect fashion.

Noooo, you say, in shocked horror! But it's true.
 
I assumed the 2 tank system was to keep the odor from coming up through the drains.... :eek:

"Noooo, you say, in shocked horror! But it's true."
---hey daddy look the guy next to us made his campsite into a swimming pool with bubbles! :-\
 
searching said:
I assumed the 2 tank system was to keep the odor from coming up through the drains.... :eek:
Click to expand...

Undumped gray water smells worse than black water in many cases, and there are traps in the plumbing to prevent those gray odors from coming up.  From what I've read, older motorhomes did have a single tank that took in everything.  We'd have to get the input of someone who worked in the RV industry probably in the early 70's when the 2-tank setup became more standard.  It does make more sense in hindsight, since gray water fills up so much faster and would cause the entire system to need more frequent dumping if they were combined.  I'm sure as Gary said that it probably used to be common (heck I still know folks who have done it ;)) to dump the gray water just about anywhere when it filled up.
 
When you go to dump, having separate tanks lets you dump the black tank first, then use the grey water to flush any remaining nasty stuff out of the hose before you disconnect it.  If the tanks were combined you'd have to rinse the hose much more thoroughly by hand.

Overfill a grey water tank and grey water will backup into your shower.  Connect your shower (the lowest drain) to a combined black/grey water tank and guess what you'll have to clean up.

If you're boondocking for a while, it's easy to get a cap with a garden hose fitting, connect a short piece of garden hose to it and drain off 5 gallons of greywater at a time into a portable container.  Then take that container to a dump station.    While you're there, get 5 gallons of freshwater (in a second, clean container) and bring it back to the rig.  Doing this daily, I find I can easily double the length of time until I run out of water and/or holding tank capacity.




 
^^ Those all seem like reasons we've come up with in recent years though... I'm wondering if any of them are related to the original change in design ~35 years ago.
 
There are still places that will request you dump the grey water on the ground.  We have been at a couple of them. However, most places if you dump on the ground you could be in trouble.  It is logical to have two tanks if only for the reasons Lou mentioned.
 
Lou,

While you're there, get 5 gallons of freshwater (in a second, clean container
Click to expand...

  I might mention to be careful about that. I've noticed quite a few dump stations that only have "non-potable" water available near the station.

    carson FL

 
Back when we had our first Class C in 1972 (35 years ago!) there was no gray tank and yes, it was "only" sink and shower water so it got dumped wherever.  We often gave trees and bushes some extra watering.  No one thought too much about it back then.  Some people even let the gray tank drain as they drove down the road.  The toilet did have a black tank and we only dumped it in approved places.  I think it's safe to say we much prefer the new gray-black tank system for all the reasons Lou mentioned, especially being able to flush out the black with the gray.  And, of course, it's more enviornmentally sound.

ArdraF
 
Two tanks...probably to do with coach weight distribution.  Also, I definitely would not want a 'one' tank system backing up into something I might be bathing in.
Overfilling the black water tank is VERY visible and no-one should get hurt, save for a couple of senses (hopefully no more than two!).  Grey water can obviously be discharged much easier on its own - without floaties...(TMI).

BT
 
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