Not near as easy to replace when your boat is relegated to life in a slip.
We had to "dive" (hard to call it diving when the water isn't over your your head) and drive a plug into the seized thru hull for the head discharge. Plug coupled with monkey poop (don't know the real name...my buddy is a navy diver and brought it over...) and we were able to change out the head hose without sinking the boat. Changing that thru hull on my next haul out.
Exercise is something the previous owners didn't seem to believe in. I'm in commercial construction, and I can tell you that building owners/maintenance personnel don't much believe in exercising valves either. Had to shut down a section of 20in steam pipe to tap into it. Had to go back 3 sets of valves before we found a set that turned/held.
