...drain and refill the system a couple times with fresh water, then...

Install the T-fitting (& cap) on the inlet (hose going to) the heater. Then flush a couple times with the fresh water hose running into the T-fitting, radiator drain plug open, motor running.

That should do it. Out with the old, in with the fresh...

Cheers!

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'91 420 SEL @ 199K, '92 SVX @ 181K, '93 SC400 @ 86K, '93 Kaw ZX-11 @ 30K, '87 F250 @ 181K , 2001 Valkyrie Interstate @ 6K, Y2K Honda NightHawk 250 with 1.5K, '88 420SEL I.@ 179K & the 2nd latest, an '88 420SEL II.@ 210K runnin' parts car, '85 F150 300/NP435