This is the short coolant hose to be replaced. You can see it leaking in this picture. This is a typical failure.

During the thermostat housing removal process you'll have already loosened the upper hose clamp on the short hose. Now loosen the lower clamp.

With the lower clamp removed you'll be able to pull the short hose off the water pump inlet.

Use a pair of pliers for grip if you need to, but it should pull off by hand.