When I say thinwall, I am referring to SDR35 or DWV, but they are not interchangeable. Both are somewhat thinner and lighter than sch 40. Four inch sch 40 is kind of a beast to handle.
I used 30 feet of glued SDR 35 through my dam as an inlet pipe (above max water level) and it works great. I buried it at a maximum depth of 31 inches in the clay.
Thin wall S&D pipe will collapse on itself with only a 5- 6 foot lift of water if there is even the slightest bend in the pipe. The S&D pipe is not intended for any pressure (high or low).
For 1.1 acres, go with 4" schedule 40 pipe with rubber couplers and be sure to make a strainer for the inlet so fish, turtles and sticks don't get sucked in that could cause a clog. 2" pipe would take a couple weeks or more to drain, where 4" will lower it in a day or two. Also, use a 45 degree elbow pointing upward on the outlet so air cannot creep up the discharge pipe and break the siphon.
Ball valves are cheap for 2"....not so cheap on 4" so forget about a valve on the pond side and use a "Test Plug" instead, on the outlet side instead of a valve. (Be sure to stand back fast after filling the discharge side of the pipe when you pull the test plug)
Test plug 
