If it's workable, get one of those Shower Drain 'Covers' that's made of rubber/vinyl, and lay it over the drain. Then, fill it w/water as HIGH as you can w/o it going into the basement. THEN, remove the Drain Cover and IMMEDIATELY fill the 'pit' again, and drain. Do it a 3rd time and even a 4th time is you want to see how many inches of rain you'd have to get before the drain actually stops draining. Of course, you won't be able to figure out how the 'surrounding underground terrain' will affect your test since it's not handling any rain (at the time of your test.) See what I mean. Well, if it can handle 16" of water in 30 minutes, I think you're OK.
My best to ya and hope this helps.
Jay J -Moderator
PS: Tieing the drain pipe to each other, I don't see a problem EXCEPT: 1) you have proper slopage, 2) the 'destination' of the water (be it a cistern or the street or whatever) can 'handle' the volume, 3) you did the drain and rock install properly. The key to #3 is that you used either Filter Fabric or Landscape Fabric in the trench BEFORE you put in any gravel and the pipe. (You did put in Fabric then 4" of gravel then 'wrapped' the fabric back over the pipe, no?) The MOST common DIY problem w/this job is the Homeowner forgets the fabric. When this occurs, the drain itself AND the perforations in the pipe become clogged w/dirt. WHen this happens, the water flow is 'obstructed', and you can end up with the problem(s) you're having. If you missed doing the fabric, I'm sorry to bring the bad news. The system may work well for a while, but after that, it's a crap shoot ...