Like many doctrines, it is not spelled out in the Bible. Rather, the doctrine is developed by taking verses and putting them together and coming to a conclusion.
I've been reading the Bible intensly for the past few months and haven't seen it in there either. I hope it's not a made up thing to comfort people because now that I have seen it in print and in a church no less, I want to find out the truth about it.
Personally, I don't think there is a purgatory. If anything, purgatory is right now living on Earth.
Here's one verse Catholics and Universalists use to support their doctrines. I will let you decide what it means.
"According to the grace of God which is given unto me, as a wise masterbuilder, I have laid the foundation, and another buildeth thereon. But let every man take heed how he buildeth thereupon. For other foundation can no man lay than that is laid, which is Jesus Christ. Now if any man build upon this foundation gold, silver, precious stones, wood, hay, stubble; Every man's work shall be made manifest: for the day shall declare it, because it shall be revealed by fire; and the fire shall try every man's work of what sort it is. If any man's work abide which he hath built thereupon, he shall receive a reward. If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire" (1Co 3:10-15).P.S. If you decide you disagree with the doctrine, there is no reason why you cannot remain Catholic and continue going to a Catholic Church.