Black tank

While using the RV or while in storage are very different answers. I would not leave fluids in the tank for extended periods while not using RV as the solids can settle and become stuck. I live in my RV with the DW and we have very large holding tanks and have been able to go for 3 weeks without dumping. It was REALLY full at that point and we really should have dumped sooner, but we did make it. A smaller coach or one not setup like the bus conversions are will not make it that long unless you are using some other bathroom facility throughout the day.