Hi John, I have the same arrangement on Grace (1983 M17 #400) and my drains failed. She lived in saltwater for 10 seasons before I bought her and corrosion took the thru-hulls out. I read the copper pipe replacement advice but 1-1/2" hose won't fit on 1-1/2" pipe (1-1/2" pipe is 1-1/2" inside diameter). The original thru-hulls appeared to be thin-walled aluminum tubing glassed into the hull. I believe the tubing was primarily the form around which the glass was placed as well as the attachment point for the flexible hose. I chose to replace them with 1-1/2" stainless steel tubing which has a 1-1/2" outside diameter and is much sturdier than aluminum. I ground out the remnants of the aluminum and glassed the ss tubing in place. I am confident that no amount of banging around will damage my new thru-hulls (at least not before the hull itself would fail). I think the original thru-hulls will last for the life of a fresh water boat (but I would still recommend checking them every few years), but they can and sometimes will corrode to the point of disintegration in salt water. I think I'll add some in line one way valves this winter to the hoses to eliminate the occasional backup of water into the cockpit. Your drains may be just fine but it would be prudent to pull the hoses off this winter and check their condition. Good luck. Mark Dvorscak GRACE