A lot of external skimmers are designed like that. With the skimmer a branch off the overflow line or the return from the sump. But in most cases the exit of the skimmer is just dumped back to the sump. I believe you would run into all sorts of problems if you had the skimmer exit under pressure. Even if it was only a little bit of head pressure. I believe you would just end up with the Skimmate cup overflowing. Water is going to go to the place of least resistance
J |