See Figure 1
Some heater hoses are joined by snap-lock fittings. There is a special tool for disconnecting these fittings. Since there are both 5 / 8 in. and 3 / 4 in. lines, there are 2 different tools: T85T-18539-AH1 ( 5 / 8 in.) and T85T-18539-AH2 ( 3 / 4 in.). Both are used with extension handle T85T-18539-AH3. There are also equivalent tools on the market.
To disconnect the fitting, use the tool to depress the plastic tabs and pull on the hose until the plastic connector clears the tabs.
To connect the hose, simply push the ends together until they snap tightly.