Building inspections stop at ground level; the drains below can hide tens of thousands of dollars in root damage, collapses and defective renovations. A pre-purchase drain inspection cameras the sanitary (and ideally stormwater) systems and reports their true condition.
On pre-1980s properties with original earthenware drains, it is among the highest-value checks a buyer can commission — the cost of the survey is trivial against the cost of undisclosed drainage failure.