Dear Newell Owner,
As Tom's answer illustrates there is no standard. His coach has two tanks and a total waste volume greater than the fresh water volume.
But, he actually may only represent a small percentage of conversions. Or his may be typical. You need to hear from all other owners, and you also need to hear from converters. Since we had two different tanks on coach #1 and a single tank on #2 there does not appear to even be a standard with a converter.
As far as capacity, I would have to say that you can control the potential for having a Kevin episode by monitoring your tank status. We have display panels in two places and audible alarms. We can also limit stored fresh water to never exceed the holding tank capacity. On our coach the auto fill limits capacity of fresh water to 80%, but we also can manually fill it until it overflows.
All of my comments are related to my Liberty, and may have no relevence to any other Liberty or converter.
Signed,
Ann Landers and Dear Abby.