Wow, they still sell those? I thought they were illegal everywhere because they don't want you flushing anti-freeze on to the street. The garden hose tee flush kits work well.
Do not use any radiator or cooling system cleaner. It will just loosen stuff up and send it into the system clogging ports.
You'd cut the heater hose to install a tee, if you bungle it, hose is maybe $1.30 a foot.