I looked up a ton of raving reviews about pool skim and really want to get one. However, i'm not too sure if my pool has an additional return inlet. I know there is a built in skimmer attached to my pool, is there anyway i can find out if there is an additional inlet? I moved my hands in the holes around the pool and i don't think i felt one that sucked water in. There is one hole with a cap on it, i'm not too sure what it does, would it do any harm if i opened the hole to see if it's an inlet?