The Prestone kit is the easiest way to do it and get it over with in one
shot. But if you want to do it the slow way where you leave the cleaner in
there a couple days, you have to run the heater so the flush is running
through the heater core also. Then when you go to drain it, you need to make
sure that you flush out the heater core also, since this isn't always part
of the open circuit of coolant flow, you may end up with some flush still in
the heater core. Meaning you should probably do the flush twice with fresh
water with a drive in between with the heater on. Then add coolant. IIWY,
I'd just get the Prestone kit and then remove the tee when your done and use
a tube to splice the two ends back together if your worried about looks.