Originally Posted by Kanadakid
When you say sound, what do you mean ? New to this and not sure my black tank lights are working correctly either. Don
As rjrelander said, when the black tank starts getting full, the sound during flushing changes from a "hollow whoosh" to a "muffled swish" (these words used only as an example) and when the black tank gets to "only a couple flushes until full" the rooftop vent stack starts to "gurgle". Our clue is the "muffled swishes" and we usually dump within a day of hearing that sound change. If we hear the "vent stack gurgles" then it's time to cancel plans, tow to the dump station and empty the black tank. When connected to a sewer connection, we keep flushing to the "gurgle" but when dry camping, I try to catch the tank before that level of fill. Our tank gauges haven't worked in at least the last 4 or 5 years. I stopped trying to keep them clean and somewhat accurate long ago.
For us, and I suppose every trailer has its own "personality" on how it communicates during flushing, but for us, the "swishing is our cue" and the "gurgles" are our WARNING !!!!!