Before you even get a septic inspector out, a walkthrough can surface real warning signs: a soggy patch or unusually lush green strip over the drainfield, sewage odor near the tank or field, gurgling drains or slow fixtures throughout the house, and any structure (deck, shed, driveway, pool) built over where the tank or field appears to be.
Wet ground or a green stripe over the field. Effluent surfacing instead of draining into the soil is a later-stage failure sign, not a first sign, and it's visible without any tools.
Sewage odor outdoors. Especially near a tank lid or over the field, this usually means gases are escaping instead of venting normally.
Slow or gurgling drains across multiple fixtures. One slow sink is a clogged pipe; several fixtures acting up the same way points upstream to the tank or field, not to one drain.
Anything built over the suspected tank or field location. A shed, deck, driveway, pool, or heavy planting over the drainfield can both damage the system and make it much harder (and more expensive) to service or replace. This is exactly the kind of thing the as-built's setback drawing would catch, if you have it before the walkthrough.
No visible lid or riser, and nobody can say where the tank is. Not a failure by itself, but it means the first real cost after closing may be locating the tank, which is billed as labor.
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Sometimes. Standing water, unusually green grass, or odor over the field are visible late-stage warning signs, but a system can also be failing with none of these visible yet. A walkthrough is a first pass, not a substitute for an inspection.
It can be. Structures over a field can damage the system and complicate future service or replacement. Confirm the field's actual location and setbacks against the permit record before assuming it's fine.
Treat it as a reason to get a dedicated septic inspection, not just the general home inspection, and to try to pull the permit record before you go further.
Reviewed 2026-08-31 against the official sources linked above (where a source is cited) or, where none is cited, left deliberately general. Laws, lender overlays and local ordinances change; confirm current requirements with the county or state agency, your lender, and a licensed inspector before you rely on this for a closing.