Sch 40 is the thick wall pipe; it's code for the main line before the backflow preventer. Class 200 pipe is industry standard after the backflow preventer. The only exception to this may be if you have very sharp rocky soil. You should always use Sch 40 for sleeves, or to go under concrete. Note: Sch 40 has more pressure loss than Class 200 and will not help to prevent freeze damage.
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