Connecting a laundry machine drain pipe directly to a kitchen sink drain pipe is generally not recommended. Doing so can lead to potential drainage issues and may result in backups and water damage. The reason why a plumber warned against this setup is because of the difference in water flow rates and potential conflicts in drainage patterns between a laundry machine and a kitchen sink.
Here's why it's not advisable:
Water Flow Rate: Laundry machines typically discharge a large amount of water at once, especially during the draining process. Kitchen sinks, on the other hand, generally have a lower flow rate since they are used for regular dishwashing and daily activities. The sudden surge of water from the laundry machine can overwhelm the kitchen sink drain, leading to backups and potential overflow.
Different Types of Waste: The water from the laundry machine contains detergents, fabric softeners, and lint, which can be different from what goes down a kitchen sink. Mixing these waste types can create clogs in the pipes, as lint and detergent residues might accumulate over time.
Drainage Patterns: Laundry machines are typically connected to a dedicated drain or a standpipe, designed to handle their water flow effectively. Kitchen sinks, however, have their drainage patterns optimized for regular use. Combining these two different drainage systems can lead to inefficiencies and backflow issues.
If you see laundry machines connected to kitchen sinks in some places, it's essential to understand that these setups might not be up to code or may not be ideal. While it might work for some time, it could lead to problems in the long run.
Instead, it's best to follow proper plumbing guidelines and local building codes. If you need to connect a laundry machine, it is recommended to have a dedicated drain line for the machine. You may consider hiring a licensed plumber to evaluate your specific plumbing situation and provide the best and safe solution for your needs. They can ensure that your laundry machine and kitchen sink drainage systems work efficiently and do not cause any problems.