Returned to home to install new replacement drain pan for main downstairs unit. Once installed and leveled I spoke with our client regarding the primary drain line and adding a second blow out service valve. She elected to install it today and also provided white vinegar to help flush and clear the line. I did ensure it was clear and showed our client a video and pictures of the primary drain line and where it leads to. She did mention that they have had repeated issues with the sink clogging in the past.