Why It Happens
What Causes Bathroom Plumbing Problems
Hair and soap residue are the first cause in this room. They mat in traps and the first feet of branch line, and Guinea's flat drain runs give the mat still water to grow in — a shower that drains 'a little slower' for a year is a mat announcing itself politely.
Toilet and faucet trouble is mostly a story of small internal parts wearing out. Flappers take a set and leak, fill valves foul with well-water grit, cartridges wear on sediment — on a well system, every one of those failures also taxes the pump, which is why bathroom parts wear out faster here than the same parts on treated water.
Failed seals let water travel where it should not: wax rings under toilets, caulk lines at tub edges, grout joints in tiled showers. The damage from a failed seal is never at the seal — it is in the floor and framing below it, which is why base leaks are 'soon' rather than 'someday' on the urgency table.
Salt air and damp work on the room's metal from outside: angle stops crust, supply nuts corrode, and the valves you will need in an emergency quietly seize. Bathrooms over under-house spaces share that damp from beneath, doubling the exposure.
Age of the house writes the rest of the list. Cottages that grew a bathroom at a time may hide galvanized stubs, improvised vents and drains laid with barely any fall — each discovered anew by every plumber, and each worth mapping once, properly, when a remodel opens the walls.
One symptom, two very different faults: a shower that slows can be choking on its own hair mat, or reporting a restriction in the branch it shares. Which one decides whether the wrench or the cable comes out.