Forget about the plug, did you say.. City water?
I hope that was the previous owner that thoughtlessly put city water in the radiator!
Always. ALWAYS use distilled water if you are mixing the coolant. Mineral deposits are the results if you don't. Same for the battery if you are still using a wet cell.
Chances are those flaky deposits are in the radiator too and not just the hoses.
Patriot Guard Rider
2000 VN750 Sere (Serendipity)
1990 GL1500 (Ole Blue)
1986 VN750 EVie (project bike, heavy custom)
VROC # 11628 / 25000-H
ARVROC # 12 Coordinator and Crowd Control
OKVROC # 18 (H)
TNVROC # 45 (H)