What about other skills and knowledge?
A professional plumber will develop lots of other skills, for example:
Pipes run under floors, so the ability to lift floorboards and relaying them,
Pipes pass through walls, so holes have to be made and patched up afterwards.
A professional plumber also needs to have some knowledge of building construction. If not, joists might be cut too deep or walls weakened by large holes and floors or walls might collapse.
Plumbers also need some knowledge of electricity, as modern boilers, pumps and motorised valves used in central heating all need electricity to operate.