Wow Jamie, thank you for this info, this explains an encounter I experience on a camping trip last year. My wife was using the bathroom sink and the water would not drain. I notice the black water tank was full but I did not under stand why the sing would not drain. We had not connected to the sewer hose because we were going to change to a better site by the ocean in two days. Once I drain the black tank, the sink drained as well. Your diagram confirms my suspicions. I do not understand why a sink would be plumed to the black tank, this make know sense to me.
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