What Newdude said.
We've only got a few of these, but PBs in our area use 3" sewer pipe so we locate the exit and usually its dammed up at the grate or pop-up because it turns into a faux skimmer when it overlows water and debris during messy monsoon storms. If the clog is not visible, we've taped the blower side of a shop vac into the exit and blow it out backwards because it's so hard to get seal on the rectangular pool-side.
It makes a small mess in the pool, but it works.
No idea if that's the setup you've been given, but maybe a place to start.