My house is being built and I want to know if the sewer clean-out pipes must stick up in the yard once the landscaping is completed?

No. Many people assume that those pipes must be left untouched after the sewer contractor has completed the work. For purposes of aesthetics and mowing, the clean-out pipes should be cut off even with the final yard grade and a flush-type of cap installed. Most are left with a cap that has a large square nut on top. Many times the nut gets cut off by mowers, which can allow debris to enter the pipe and cause a blockage. The ONLY pipe which must be left (12″ to 18″) above the ground surface is the vent pipe with a breather cap on top, which is the first pipe outside of the house.