Pool came with new house. Seller was an investor who never lived in the house and didn't maintain the pool (renters did), so I don't know the pool history. Is this a return that's been capped off? We only have 2 returns, so a 3rd could really be beneficial for circulation in this big pool. Is there any risk to taking the plug out? What are possible reasons they capped it? What else could it be besides a return?