Our trailer is a 1973 model Airstream. It has no grey water tank, only a black water tank. When we first bought our new home, Lauren and I believed that the absence of a grey water tank meant that the two were combined into the black water tank. In fact, this is not the case. Today, poring over the service manual, confounded with sewage issues, we realized how important this distinction is.
Let me explain. Rocking like we do, sans grey tank, the holding tank for effluent is above the drainage pipes from the sinks and shower. There is a holding tank valve, but it is also above these drainage pipes. So, when we arrive at a park and remove our sewer cap, grey water rushes right out--there is no valve to stop it. The valve only seals off the black water holding tank. This allows us to pull over on the side of the road, wash our dishes, brush our teeth and take a shower and dump all that water on the side of the road without loosing any of the nasty. And, if you think about it, that makes perfect sense. It's potable water to begin with and it's no worse than bathing or washing camp dishes in a creek.
Today, however, we have different notions about what matter of discharge is appropriate. And that's totally fair. Maybe the RV crowd has abused our collective trust. Maybe, more likely, we've become more familiar with how gross each other can be and any kind of dumping isn't worth the risk. Which explains why, starting in 1975, all Airstreams were manufactured with grey water holding tanks.
The confusion Lauren and I have experienced on this trip out West is due entirely to the fact that we grew up in a grey water holding tank world. We're grey tank natives. Now that we understand the intent of the pre-1975 engineers, now that we're in that head, we can totally understand the schematics and correct and prevent all matters effluent.
It's amazing to me how our cultural and generational bias affected our ability to interpret technical drawings.