Quantity Matters

A friend asked why there is not a single holding tank for gray and black water. I couldn't answer him. Can you tell me?
Kay, (Daniels, WV)

 

Kay, though the industry-adopted “standard” for building RVs does not specifically mandate two individual holding tanks, most manufacturers and virtually all RVers prefer the separation of liquid and solid waste. In the old days, many RVs only had one single holding tank for solid waste with the gray water by-passing the tank altogether. Once tanks for gray waste systems became commonplace, manufacturers simply decided to keep them separate though it is permissible to have one gray fixture plumbed to the black water holding tank.

Some large coaches actually have three holding tanks, especially those equipped with a washer/dryer. My thinking is that if a motorhome only had one tank, it would fill rather quickly since the draining sinks and showers would fill the single tank rapidly; unless that one tank is quite large. And therein lies the most probable second reason for separate holding tanks. It’s easier to mount and design a motorhome around two smaller tanks that one large super tank!