It’s generally not advisable to dispose of dirty diluted mortar water down a laundry sink or any plumbing system. Mortar water can contain cement particles and other materials that could lead to clogs over time. Additionally, it may alter the pH of your plumbing system and potentially harm your plumbing infrastructure.
A better option would be to let the mortar water settle, allow the heavier particles to settle at the bottom, and then dispose of the clear water carefully. Solid waste should be disposed of according to local regulations, often involving disposal at a construction waste site or a landfill that accepts construction debris. Always check your local guidelines for proper disposal methods to avoid any environmental damage or plumbing issues.