I am in the process of widening my asphalt driveway. There is a gentle slope to the side so I am building a small retaining wall out of segmental concrete wall block and my asphalt driveway will be replaced with pavers. One of the downspouts runs in a pipe under a bed of pachysandra and terminates right next to the "upside" of the driveway. Water tends to pool in this area so I am going to extend the pipe under the driveway, under the retaining wall that I am currently building, and use a pop-up at the end (I've read the threads here about pop-ups. I live in Maryland and I installed one of these 4 or 5 years ago and have had no problems at all). The existing pipe is 4" thin wall, but I want to use the 4" thick wall for the new pipe I am installing. I am also going to install some kind of a drain in the middle of my new wider driveway and I plan on joining that pipe to the pipe discussed above so they drain to the same pop-up. My questions: 1) How do I connect the thin wall pipe to the thick wall pipe? 2) How do I connect the thick wall pipe to the pop-up (the pop-ups I've seen at my local stores are thin wall and do not fit with the thick wall) 3) What type of drain should I install in my driveway? Plastic? Metal? Round? Square? 4) Will the type of drain identified in question 3 connect easily to my thick wall 4" pipe? I have attached a current photo of the project. Thank you!