Thanks Ron for explaining this.
So, we definitely must pray for the souls in Purgatory AND we can also ask the souls in Purgatory to pray for us, right?... it sounds like a good deal (in the good sense of the word). "Souls in Purgatory, please pray for me regarding __________ and I pray for you to go to Heaven ASAP".
Perhaps they are anxious waiting for us to ask them to pray for us - which help us and helps them in their tasks.