[Motor31]

Our black tank sensors have been useless since 2 months after we got the rig. That's no big deal to us as we know from use that we can go for 8 days before dumping. I use a clear plastic elbow on the line to determine when the flush is complete. I usually close the valve for a minute then drain it with the flush going to build up water and clean out the tank at least 3 times. When done I close the valve for 15 to 30 seconds depending on water pressure / flow to add water to the black tank for the next week. We also put a couple loads of laundry worth of water in the grey tank to flush out the hose.