Just an idle question ? Why do RV's have separate black and grey tanks. I have a septic system at home; black and grey wastes flow through the same pipes into the same tank; eventually to the field.My unit originally had 40 gal grey and 40 gal black. 40 gallons of grey is good for 4 days, 40 gallons of black for 10 days. Not very sensible.Is this possibly a holdover from when many units had a black tank, but were designed to essentially dump the grey water on the ground?As I said, just an idle question, but inquiring minds want to know. Any thoughts or ideas?Doug

I personally think it's better to separate, especially if the tanks are small. I don't mind hauling grey water in a tote to the dump, rather not tote black. And like you my septic is all in one at home, but irrelevant.

...this possibly a holdover from when many units had a black tank, but were designed to essentially dump the grey water on the ground?--------------------------------------------------------------------------Yes, in the past. Now it's more likely it's a weight distribution thing.

RVs use to have just one waste tank......black/grey all went to that one tank (Small campers/truck campers dumped grey---just a black for toilet)THEN folks wanted bigger.....more bells/whistlesSpace limited so separate tanksThen more, more........Space still limited so more tanks added (black/grey/galley)Then more, more........So split baths------double black/double grey/galleyThere is only so much room for tanksI have black/grey/galley that all tie into to a common drain header so I added an extra dump valve on that header. (there is a twist on version)With it closed and all tank valves open I have 128 gallons of waste capacityYep.....just like a residential waste system. All together.They are WASTE tanks. Grey just as nasty/smelly as black----worst due to food debris, grease/oils, hair, sloughed skin, body oils etc.I run out of fresh water before filling waste ---good for 7 days

You have to go back PRIOR to 1978 to see any RV that had 1 Waste tank(There were some, very few, that had single tanks after 1978) . So, Is your question relevant after almost 40 years? Probably not. Weight distribution is not a factor. The plain fact is, most people want 2 tanks. You will put more waste in the Gray tank than the black tank. So dumping the Gray just makes more sense and you can go longer if you do not fill a single tank faster due to all gray and black going to a single tank. AND it gives the Black tank chemicals time to completely dissolve the Black waste. Doug

doughere wrote:My unit originally had 40 gal grey and 40 gal black. 40 gallons of grey is good for 4 days, 40 gallons of black for 10 days. Not very sensible.Of course it's sensible. With just my wife & I using our camper and just the toilet feeding the 30 gal black water tank we could camp for at least two weeks straight without having to give any thought to off loading the contents of the black water tank. The 30 gal grey water tank I typically off load every day or two and because it's MUCH easier to deal with grey than black no way would I want a combined black & grey tank.

Black/Grey tanks | Good Sam Community

20 Replies

RJsfishin
Explorer
Oct 18, 2016
I guess some airplanes are still that way.
GordonThree
Explorer
Oct 18, 2016
beemerphile1 wrote:
GordonThree wrote:
BFL13 wrote:
GordonThree wrote:
That's right, no black tank, just a hole in the floor.

Ahh, the good old days!

Do not flush while train is standing in the station

Hahah good one! :)

There are still some vintage train cars in use with that system and that sign. When you do flush the waste drops straight to the road underneath.

Hopefully there aren't any vintage coach working the same way.
beemerphile1
Explorer
Oct 18, 2016
GordonThree wrote:
BFL13 wrote:
GordonThree wrote:
That's right, no black tank, just a hole in the floor.

Ahh, the good old days!

Do not flush while train is standing in the station

Hahah good one! :)

There are still some vintage train cars in use with that system and that sign. When you do flush the waste drops straight to the road underneath.
GordonThree
Explorer
Oct 18, 2016
BFL13 wrote:
GordonThree wrote:
That's right, no black tank, just a hole in the floor.

Ahh, the good old days!

Do not flush while train is standing in the station

Hahah good one! :)
RJsfishin
Explorer
Oct 18, 2016
My black determines when and how often I have to move....every 17 days.
My grey seems goes forever, while any bushes and trees near me, look real healthy.
But besides that mine has a 2" crossover pipe w/ ball valve between the 2 identical 42 gal tanks, just for those rare times when there ain't no trees or bushes !
Dave_H_M
Explorer II
Oct 18, 2016
doug, you can combine them if you want. Just put a spin on valve on the main dump and pull both tank levers open.
SaltiDawg
Explorer
Oct 17, 2016
GordonThree wrote:
My 100 year old grandmother brags to this day about the ingenuity of my grandfather who installed electrics and a flush toilet in their first camper. He cut a hole through the floor and bolted down a porcelain throne. He'd just fill up the water tank when they needed it, and gravity did the rest. That's right, no black tank, just a hole in the floor.

Ahh, the good old days!

Years ago I worked out of an Office in a Building on a pier at Puget Sound Naval Shipyard in Bremerton, Washington.

During WWII the building had been the Women's Head or Bathroom.

You could still see the indentations under the linoleum where each toilet had sat... probably 75+ toilets dumping into Puget Sound.

Earlier when I was going to sea on submarines, it was standard practice on the 12-04 AM watch to use air to blow the contents into the river. (No longer done.)

Let me assure you the Security Guards on watch topside, depending on wind direction and the tide, were not happy.
braindead0
Explorer
Oct 17, 2016
Nobody wants a mix of black and gray water to back up in the shower.....
BFL13
Explorer II
Oct 17, 2016
GordonThree wrote:
My 100 year old grandmother brags to this day about the ingenuity of my grandfather who installed electrics and a flush toilet in their first camper. He cut a hole through the floor and bolted down a porcelain throne. He'd just fill up the water tank when they needed it, and gravity did the rest. That's right, no black tank, just a hole in the floor.

Ahh, the good old days!

Do not flush while train is standing in the station
DutchmenSport
Explorer
Oct 17, 2016
Big single tank... heavy, all in one spot, takes lots of space ... somehow.

2 or 3 smaller tanks? probably holds the same amount, but smaller tanks can go into smaller areas, hold less per tank, don't weigh as much per tank, and the weight can be distributed over a wider area.

Or .... someone decided they could make more money installing 3 tanks instead of just 1??? ;)