[JRTJH]

Several comments/questions in your last post, so I'll try to cover them. Sensors are not reliable. Most of us have simply learned to ignore them. We learn how much water we use and how many days we can go when dry camping and we "live by the calendar" rather than relying on the status indicator panel. Even the battery indicator is "inaccurate" when you consider that there's only 1 volt difference between a battery at 100% charge and one at 30% charge. So what "good" would a 75, 50, 25 % light do (other than fool you into believing you're OK when really you might not be)... As for changing them, if they are expansion sensors you can change them out, if they are "spin-welded" into the tank, they're a permanent part and you'd be better off installing a new set adjacent to the defective ones. Or, honestly, just ignoring that part of the system and relying on the calendar...... Even new sensors will "foul" with a bit of tissue or waste and give a false reading. None of the OEM sensors are reliable to any degree where an experienced camper would rely on them.

All of the tanks "merge" into that one 3" dump connection. The black tank is a 3" tube, the galley (kitchen) and gray (bath) tanks "T" into that pipe and are 1.5" lines. There is no "check valve" and nothing to prevent black tank effluent from "backing up into the gray tanks" except for a slight "gravity incline" on those pipes. Most of us leave the gray valves closed, dump and flush the black tank, close the black valve, then open the nearest gray tank, allow it to empty and then open the furthest gray tank and allow it to empty. The gray water will "flush the lines" of black effluent. Once finished dumping, close the gray valves and replace the cap on the 3" terminal fitting.

Some of us (when dry camping and without access to water to use the black tank flush) will use gray water to "partially fill the black tank", then close the gray tank valve and dump the black tank a second time. That helps to flush any remaining waste from the black tank and with two full gray tanks, is easy to do, but isn't something to try unless you're familiar with your system and know how long each gray tank takes to empty. I suppose that would be "second level tank dumping" and mastering "first level tank dumping" would be in order before trying it.....

You're right, "if a guy forgot...." after a couple of mistakes, you'll get your routine down and you "remember not to forget" when you're dealing with black tank effluent..... One or two "unpleasant experiences" and you learn quickly what to do so you don't "forget"..... Any of us can assure you that you won't be "the only one" and most of us will also attest that we don't forget any more..... Or at least we work "diligently" to try not to forget !!!!!