What type of appliance is used to combine two hose lines into one?

The correct answer is the Siamese connection. This appliance is specifically designed to join two separate hose lines into a single line, allowing the combined flow of water from both sources. It is crucial during firefighting operations when a higher volume of water is needed than what a single line can provide.

Siamese connections typically have two male inlets on one side and a single outlet on the opposite side, which helps connect two hoses coming from different engines or hydrants. This ability to combine multiple water sources into one line effectively enhances firefighting capabilities and can be instrumental in quickly increasing the available water supply.

The wye connection, while functional for other purposes, divides a single supply line into two smaller ones rather than combining two lines into one, making it unsuitable for this specific need. The water thief also serves to draw water from a larger line but does not combine two hose lines into one. A gated wye is similar to the wye connection but includes valves to control flow to each of the two lines but still does not serve the purpose of merging two hoses into one. Thus, the Siamese connection is the appropriate choice for combining two hose lines.