The answer to 'water line replacement won't flush' is that a blockage in the new water line is likely preventing proper flushing. This could be caused by debris, mineral buildup, or a kink in the line. The symptoms may include slow or no water flow, gurgling sounds, or water backing up in fixtures.
To resolve this issue, you'll first want to check for any visible blockages or kinks in the new water line. If you can't identify and clear the blockage yourself, it's best to call a professional plumber. They have the tools and expertise to properly diagnose and fix the problem, ensuring your new water line is functioning correctly.