All waste liquid that arises in the autosampler is released through the silicone waste tubing at the left side. If this tubing is blocked the waste liquid is released through a safety overflow at the bottom of the autosampler.
To ensure a proper runoff of liquid the waste bottle should always be placed below the autosampler as the outflow is gravity-driven only.
Also, if the waste tubing is narrowed at some point this can result in back-pressure and backflow. A narrowing can be caused by a kink in the tubing or if a tubing with smaller ID is connected.