Which of these fixtures requires an overflow?

A bathtub requires an overflow to prevent water from spilling over the sides during filling. Overflow systems are designed to ensure that if the water reaches a certain level, it will flow into a drain rather than overflow onto the bathroom floor, which could cause water damage and create a safety hazard.

The other fixtures typically do not require an overflow. For instance, lavatories generally have a built-in overflow drain, but in this context, bathtubs are more commonly recognized for needing an overflow feature due to their larger volume and the potential risk of overfilling. Shampoo sinks generally have lower capacities and drains that are designed to handle the water flow without the need for additional overflow systems. Kitchen sinks similarly are designed to drain efficiently, often using disposals or other mechanisms to handle overflows, but do not have a standardized overflow feature like bathtubs do.