On plumbing, the price comes from the number of connections and outlets, not from metres of pipe — which is why two bathrooms of the same size can differ twofold.
Sections
Strip-out; supply pipework in linear metres by diameter and material, with manifold, isolation valves and the meter set; waste pipework with stack connections and falls; connections counted per fixture; chasing and core drilling; waterproofing to wet areas as its own line, never "included"; fixture installation per unit; pressure and flow testing before the walls are closed; and fittings and brackets priced separately from pipe.
Waterproofing is where saving money comes back a year later. If the client wants it out, record in the estimate that it was excluded at their request.
Say what happens to the walls
State what is included — pipework, connections, testing — and what is not: filling chases, plasterboard boxing, tiling, access hatch finishing. That boundary is the usual source of disputes with the finishing crew.
See the estimate template and the apartment renovation estimate.