The Rio 800 RVT pump (recirculating venturri) on that skimmer could be used to help remove air bubbles that might build up in an overflow box, BUT if the pump is also running the skimmer, it will reduce the skimmer's performance because it would be sucking more than just air through the air intake tube. Plus, if the skimmer is in a sump, I'm not sure how much it'll help an overflow box at that distance.
Not that a seller would neccessarily mention this to a buyer, but if the person asking is only looking at it for the pump, the pump can be bought new for $20. And, there's a couple of us setting up a reef tank at work, and the skimmer brought in was running on that same model pump. The pump (used) failed within a month of running it on our work tank, but I cannot say how much use it had before we put it on this work tank. Anyways, my point is that once it failed, I disassembled it and the impeller paddles had separated from the magnet. Personally, I thought it was a very poorly crafted impeller assembly -- very weak. We considered replacing the impeller, but the cost of a replacement was near 1/2 that of the pump new. A quick search for some alternatives led us to an aftermarket venturri upgrade for the Maxi-Jet line of pumps that increases air intake to a level suitable for using the MJs on a skimmer. So, we decided to go with that ($4 online before shipping) since the MJ pumps have a better reputation for durability / longevity than the Rio pumps.
