How to clean the Chery qq3 heater water tank if it is clogged?

The heating water tank of this car has two pipes on the firewall, which are installed inside the instrument panel. To clean, you need to remove the pipes, connect one end with tap water, and the other end, throw it outside. It is more troublesome to replace it, and you need to lift the workbench. This situation has nothing to do with the slow rise of the water temperature. The general reason for the slow rise of the water temperature is that the thermostat is opened too large, or it is not installed. Need to check installation