Thought I pass this along for back flushing your black water tank.
I have a Scamp
13 and found it was difficult to guess how much water I was using with my Valterra Flush King to back flush my black water tank. Then I found this water meter on Amazon which tells me within reason how much water I am using. There are 2 readings, the upper reading can be used and reset between flushes and the lower reading the total amount of water used, which can be reset as well. The device is made by "Save A Drop"
This way I am sure not to expect any surprises on the bathroom floor when I am finished. I usually use 3.5 gal each time I do a back flush until I am sure I have flushed it thoroughly.
The other device connected to the meter is a back flow preventer.