Hi Peg,
Many PCs have a smaller grey tank than a black tank. Our 2350 has the same situation. It is "extremely" simple to flow 50% or more of the grey tank into the black tank by a simple throw of two switches, the grey tank valve switch first, the black tank 10-15 seconds following. Wait about 20-30 seconds and then close both valves. Since you don't own a PC yet, it will be "foggy" for you to understand. But trust me....you won't have a problem with that matter at all. Irene and I take back to back showers. I shower first. Once dry and dressed, I go out and blend the grey tank into the black tank so she can finish her shower without a shower pan with bath water that won't go down the drain.
If ordering your PC, I advise to pay a tiny bit more to have Phoenix add redundant tank valve switches inside so you don't have to go outside. I hope to be installing redundant switches myself sometime this year in our 2007 2350.
Welcome to the Phoenix forum!
Ron Dittmer