Moved to Salem forum, hopefully you will get more help here.
One thing I will never understand. People want to know what their holding tank capacities are. They are usually the same, or only 1o gallons more than the fresh water tank.
Since you have no way of measuring the water from the sink, the shower, or anything else, what does it matter? If you are boon docking, and a have a full fresh water tank, and water heater full, there is no way to fill both holding tanks.
Now if you are looking to purchase a blue boy, sewage tote, I understand the question.
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic
2008 Work and Play 18LT