It’s not all just poopoo peepee stuff. A lot of plumbers do mechanical work in commercial buildings, boiler retrofits, repiping, construction. I’m in commercial HVAC and work with a bunch of plumbers whose skills and scope of work have great overlap with mine. We offer similar services, subcontracting each other to our own customers, just they do more of the gas fired work and fix leaks in heating loops and I do the AC/Refrigeration stuff