Separate pipes for black and gray tanks

I'm on my second trailer with 2 gray and 1 black tank. There is one dump port with separate black and gray valves and then another port for the aft gray tank. I always looked at it as an advantage because of the extra capacity. The only time I bother with using a T is when I have full hookups and will be there long enough to dump more than once.

PawPaw_n_Gram wrote:
The black tank is almost always located directly under the toilet. RVs don't have the water flow from the toilet for a run any distance to the tank.

Another clue is often the size of the pipe running to the dump outlet. A black tank pipe will be 3 inches in diameter. A gray tank is normaly 1 1/2 or 2 inches in size.

If it were my rig - I would get some food coloring and make sure I had a clear 45 degree elbow to attach at the outlet.

I'd go to a dump location, empty the tanks. Then put water colored with one color into the toilet. Open the dump valves in turn and see which allows that colored water to drain. Repeat with the shower and a different color, and with the kitchen sink with a third color.

That way you will be totally positive which handle/ valve drains which tank. You can change labels if needed.

You might also want to try it with a fourth color and the bathroom sink - just to know if that drains into the black tank or the gray tank. Some rigs do it either way. On my current rig, when I look under the sink, I see the drain going off at a 45 degree angle to under the shower, not directly down into the black tank, so I know the water goes into the gray tank.

You have given me a lot of good ideas. I really appreciate it.

The black tank is almost always located directly under the toilet. RVs don't have the water flow from the toilet for a run any distance to the tank.

Another clue is often the size of the pipe running to the dump outlet. A black tank pipe will be 3 inches in diameter. A gray tank is normaly 1 1/2 or 2 inches in size.

If it were my rig - I would get some food coloring and make sure I had a clear 45 degree elbow to attach at the outlet.

I'd go to a dump location, empty the tanks. Then put water colored with one color into the toilet. Open the dump valves in turn and see which allows that colored water to drain. Repeat with the shower and a different color, and with the kitchen sink with a third color.

That way you will be totally positive which handle/ valve drains which tank. You can change labels if needed.

You might also want to try it with a fourth color and the bathroom sink - just to know if that drains into the black tank or the gray tank. Some rigs do it either way. On my current rig, when I look under the sink, I see the drain going off at a 45 degree angle to under the shower, not directly down into the black tank, so I know the water goes into the gray tank.

PawPaw_n_Gram wrote:
The pictures I see on the web of models for sale show two dump valve pulls in the compartment on the road side near the dump connector. They also show a dump valve handle on the second tank dump connector. That indicates a black and gray tank in the front, and a gray tank in the back.

Verify that yourself - that there are three dump handles.

I found a copy of the 2014 brochure for the Voltage. The 3970 is listed with 160 gallons of fresh water, 48 gallons of black water and 96 gallons of gray water.

When you see specs that show twice as much gray water as black water - it indicates two gray water tanks and one black water tanks.

RV manufacturers vastly prefer to have the tanks the same size, so adding three tanks in different locations means they fit into an identical sized space under the floor between the frame rails.

I'm surprised at the fresh water capacity of the rig, but again the two tank likelyhood is high. 160 gallons of water is heavy - over 1,300 lbs. In one tank, a partial load could create surge issues while traveling.

(That rig has potentially 2,537 lbs of water with all tanks full. That is a LOT of water to haul around.)

But you need to verify those items by inspecting the rig. Look for possibly two fresh water pumps - that would confirm two fresh water tanks.

There are 2 handles in the compartment. One says Bath, one says Kitchen. So those make sense for 2 gray water tanks. Further back, right at the other outlet is another handle, which I assumed to be the black tank valve. I will have to verify.

I will look for the fresh water tanks. One thing I do like is the fresh water tank has a dump valve also. Our older rig didn't have that.

The pictures I see on the web of models for sale show two dump valve pulls in the compartment on the road side near the dump connector. They also show a dump valve handle on the second tank dump connector. That indicates a black and gray tank in the front, and a gray tank in the back.

Verify that yourself - that there are three dump handles.

I found a copy of the 2014 brochure for the Voltage. The 3970 is listed with 160 gallons of fresh water, 48 gallons of black water and 96 gallons of gray water.

When you see specs that show twice as much gray water as black water - it indicates two gray water tanks and one black water tanks.

RV manufacturers vastly prefer to have the tanks the same size, so adding three tanks in different locations means they fit into an identical sized space under the floor between the frame rails.

I'm surprised at the fresh water capacity of the rig, but again the two tank likelyhood is high. 160 gallons of water is heavy - over 1,300 lbs. In one tank, a partial load could create surge issues while traveling.

(That rig has potentially 2,537 lbs of water with all tanks full. That is a LOT of water to haul around.)

But you need to verify those items by inspecting the rig. Look for possibly two fresh water pumps - that would confirm two fresh water tanks.

PawPaw_n_Gram wrote:

Doss wrote:
One thing I noticed on the walk through is that there is a separate outlet pipe for the gray tanks and the black tank.

Looking at the floorplan and pictures of that model - this isn't completely accurate.

You have one dump outlet for the kitchen 45 gallon gray tank. You have another dump outlet for the bathroom 45 gallon black tank and the 45 gallon bathroom black tank.

The front dump outlet is just like what you've always had before. You just have an additional gray tank farther back for the kitchen with it's own dump.

You also likely have two 80 gallon fresh water tanks - one in the front and one near the kitchen - but they are plumbed together so you only need one fill.

that is really good info my friend. You probably saved me from a big suprise

Doss wrote:
One thing I noticed on the walk through is that there is a separate outlet pipe for the gray tanks and the black tank.

Looking at the floorplan and pictures of that model - this isn't completely accurate.

You have one dump outlet for the kitchen 45 gallon gray tank. You have another dump outlet for the bathroom 45 gallon black tank and the 45 gallon bathroom black tank.

The front dump outlet is just like what you've always had before. You just have an additional gray tank farther back for the kitchen with it's own dump.

You also likely have two 80 gallon fresh water tanks - one in the front and one near the kitchen - but they are plumbed together so you only need one fill.

I have thought about putting a tee in. I guess we will see how it goes after our first trip

Army11Bravo wrote:
My silly trailer has 2 separate outlets. I considered plumbing them together, but haven't. I dump black first, move the hose and dump gray second, then move the hose one last time to dump black with sprinkler in the tank running.

It's an inconvenience, but not too bad.

My last rig had the dual outlet set up. I despised it, however I learned to live with it.
Dual outlets would be a potential deal breaker on all future RV's.

My silly trailer has 2 separate outlets. I considered plumbing them together, but haven't. I dump black first, move the hose and dump gray second, then move the hose one last time to dump black with sprinkler in the tank running.

It's an inconvenience, but not too bad.