Originally Posted by type901
I previously asked about the placement of the black tank - if it could be in a different location from the toilet. I got a reasoned response that it should be under the toilet because the solids don't need as much water to make it to the tank. Make's perfect sense.
But it leads to another question. If the black tank is on the curb side, or in this case about halfway from center to curbside, and the valve is on the road side, what is the composition of the parts from the tank to the dump valve? It would appear that its just an elbow from tank to pipe, and then pipe to slide valve. It seems to me that the pipe from the tank to the dump valve fills up first, kind of additional holding volume. But it also seems to me that this may create blockage. Or is a system not as simple as described? Am I missing something/misunderstand how it works?
The valve would be right where the tank outlet is located. If you use T-handles to operate the valve, there would be a push-pull cable running from the T-handle to the valve. Because the valve is at the tank, the pipe or hose (I'll call it a pipe for now) in between the tank and the slinky isn't always full and solids don't get a chance to clog the pipe.
When you first open the valve, the water rushes out of the tank into the pipe, carrying the solids with it. (Side note, if your black tank isn't full when you want to empty it, top it off with water before emptying; it will empty better.) The black water keeps right on going from the pipe to the slinky, and doesn't collect in the pipe. Assuming you've designed and installed it correctly so there's a slope all the way from the black tank to the fitting where you attach the slinky.
Your gray tank should connect to the same pipe at a "Y" fitting, so you only have to connect your slinky once, not move it from one tank to the other. Gray tank would have the same valve setup, a valve right at the tank outlet operated by a push-pull cable. Because graywater contains a lower proportion of solids (hopefully nothing more than small food particles that get past your sink strainer) you don't need as much slope to ensure adequate drainage in the discharge pipe; another reason above-the-floor black tanks are preferred, while below-the-floor gray tanks are the norm.