Well, even if you do not
have a vacuum type cleaner that does not mean the pool is not plumbed for one
Is there a suction valve or return valve that is closed that could be attached to one of the holes?
Is the hole directly below the skimmer? Could be an equalizer line and just plumbed up to the 2nd hole in the bottom of the skimmer.
Wait your pool was finished 2.5 months ago? why not ask the builder what they did.