I wanted to use the vacuum here: http://www.thingiverse.com/thing:941551 But I didn't want to glue the quick connect piece to the Intex cover that usually connects to the outlet that goes to towards the filter pump. Instead, I decided to make this piece, which replaces the Intex piece.
After I designed it, I found: http://www.thingiverse.com/thing:179352 which is essentially the same thing I have uploaded here. I almost just downloaded it instead of printing mine. Then I saw that it was untested and didn't include the source .scad file. I tweaked my design and started it printing.... and at the same time (give or take the 8 hours I was away from Thingiverse), the author uploaded the .scad file! JJanssen's thing is still untested so I'm publishing my version. I've tested it my version and it works well.
You will need an o-ring over the quick connector. I used one measuring 11mm (7/16") ID, 16mm (5/8") OD, 2.5mm (3/32") thick. You can get 100 for around $2.50 on Amazon (search for #111 o-rings) or around 10 for around $2.50 at most hardware stores.
If you are modifying the .scad file, make sure you have the knurling library and the metric thread library.
Update 7/26/2016: Oops. Looks like the threads weren't actually attached to the rest of the adapter (though they must have been close enough to print as one or for Cura to fix it automatically). I've updated both the .scad and .stl files.
Note that if you have two outlets that run from the pool to the filter/pump (plus the third that runs back from the pump to the pool) then you need to either stop up the outlet that you don't have the printed adapter hooked to (which is what I have done) or print two adapters, hook them both to a Y adapter, and then to the vacuum piece (this should work better but I have not tested it).