Your Toyota heater hoses are preformed so they will follow a predetermined path from the engine compartment to the heater core. This is done on purpose so the heater hoses do not make direct contact with other components in the engine compartment.
With each pair of heater hoses on your Toyota there is a supply and return hose. The supply is mounted to the engine and is the hose that is exposes the greatest level of stress. Both of the hoses are made of reinforced polymer that are made to last for many years, but the hot coolant that flows through them causes them to break down in time.
The most common reason for a leak from a Toyota heater hose is after time they balloon up in which the walls of the hose become thin. This is where the breach in the coolant system will occur. The most likely place for this ballooning is where the supply heater hose is directly connected to the Toyota engine block. This is the location that is exposed to the greatest level of heat on a constant basis. If this is the place of your coolant leak then a puddle will be created under the engine where the vehicle is parked.
To actually observe the leaking hose, the Toyota owner should conduct their inspection just after the engine is turned off. This is the time when the coolant system will have the greatest level of pressure in it. Before the engine is turned off, the heater should be on so the coolant will be flowing through the heater hoses so the leak can be located. This leak should appear like a small fountain of coolant coming out.