They undergo purification.
Purgatory isn’t a place; it is a process. Since nothing impure can enter the Kingdom of God, anyone judged worthy of entering it that is in a state of any sin in any way must be purified.
Purgatory is not expressly called out in Scripture, but we must come to the conclusion that it exists simply because of those two conditions.
How exactly does this work? Are they totally passive and something is done to them, or are they actively involved in this purification process.
Purgatory isn’t a place; it is a process.
If purgatory is not a place than that begs the question does it exist?
If purgatory is a process than the question is when does this process occur.
Purgatory is not expressly called out in Scripture,..
I'm aware of that. I've learned there are a great many things RC's and EO believe in that are not in Scripture. I'm sure that's part of the reason behind their disdain for Sola Scriptura. It would be too limiting.