Short answer: a house with a 浄化槽 (jōkasō) treats its own wastewater in a tank under the garden instead of sending it to a public sewer. It is normal in rural Japan and not a defect — but by law you must pay for regular maintenance, an annual clean-out and an annual inspection, and you pay the electricity for an air pump that never switches off. Budget roughly ¥50,000–100,000 a year for a typical 5–7 person tank, plus a one-off replacement (¥800,000–1,500,000 or more) if the tank is an old single-treatment type or has failed.
A jokaso is an on-site wastewater treatment tank regulated by the Septic Tank Act (浄化槽法). Bacteria in the tank break down sewage; the treated water drains to a ditch or soakaway. On a listing, look for:
| Listing term | Meaning |
|---|---|
| 浄化槽 | Septic tank present (the good case if it is a 合併処理浄化槽) |
| 合併処理浄化槽 | Combined-treatment tank: treats toilet and kitchen/bath water. The current legal standard for new installs |
| 単独処理浄化槽 | Single-treatment tank: toilet only; kitchen and bath water go untreated to the ditch. No longer permitted for new installs since 2001 and the law asks owners to replace them |
| 汲み取り | No tank at all — a vault toilet emptied by truck. Older and cheaper again |
| 下水道 | Connected to a public sewer. No tank costs |
| 排水: 側溝 / 河川 | Where treated water goes; relevant for odour and neighbour issues |
If the listing says nothing, ask 排水方式は下水道・浄化槽・汲み取りのどれですか？ ("Is drainage public sewer, septic tank, or vault toilet?") and, if a tank, 合併ですか単独ですか、設置年と人槽は？ ("Combined or single? Year installed and capacity in persons?").
The Septic Tank Act places three duties on the owner or manager of a tank (浄化槽管理者), which becomes you on purchase:
| Duty | Japanese | Frequency (typical household tank) | Who does it |
|---|---|---|---|
| Maintenance / servicing | 保守点検 | At least every 4 months for a small combined tank (i.e. 3 or more visits a year); the exact interval depends on tank type and size under Ministry ordinance | A registered maintenance contractor (保守点検業者) |
| Clean-out (sludge pumping) | 清掃 | At least once a year | A municipally licensed cleaning contractor (清掃業者) |
| Statutory inspection | 法定検査（11条検査） | Once a year; plus a one-off inspection (7条検査) within months of a new installation | The prefecture's designated inspection body (指定検査機関) |
Sources: Septic Tank Act (浄化槽法) Art. 7, 10 and 11; Ministry of the Environment, 浄化槽サイト. Skipping the statutory inspection is an offence, although enforcement is by prefecture and in practice starts with a reminder letter.
Ask the seller for the last inspection certificate (法定検査結果書) and the maintenance contract. A tank that has been serviced on schedule is a good sign about the house as a whole.
Prices are set by private contractors and vary by prefecture and tank size. Typical ranges quoted by contractors and prefectural associations for a 5–7 person (人槽) combined tank:
| Item | Typical annual cost | Notes |
|---|---|---|
| Maintenance contract (3–4 visits) | ¥15,000–40,000 | Often billed as a yearly contract; includes adding disinfectant tablets |
| Clean-out (1 pumping) | ¥20,000–40,000 | Priced by volume removed; larger tanks cost more |
| Statutory inspection | ¥5,000–10,000 | Set by the prefecture's inspection body |
| Electricity for the blower | ¥8,000–15,000 | A 30–80 W pump running 24 hours; more for large tanks |
| Blower replacement | ¥20,000–50,000 every 5–10 years | The most common repair |
| Total, typical year | ¥50,000–100,000 | Comparable to sewer charges in many towns, sometimes higher |
Compare with a public sewer, where you pay a monthly usage charge (下水道使用料) tied to water consumption, typically ¥2,000–5,000 a month for a small household. Over a year the two are in the same range; the difference is that the jokaso costs arrive as a few larger bills and depend on you arranging contractors.
Under the Sewerage Act (下水道法), once a public sewer becomes available in front of the property, the owner must connect the building's drainage without delay (Art. 10), and a vault toilet must be converted to a flush toilet connected to the sewer within three years (Art. 11-3). The connection cost — digging from the house to the street main and abandoning the tank — is the owner's, typically several hundred thousand yen, though some towns subsidise it. In addition, most municipalities charge a one-off sewer contribution (受益者負担金) when the sewer is laid, calculated on lot area.
Before buying, check the town's sewerage plan (下水道整備計画): if the street is scheduled for a sewer in the next few years, a brand-new tank would be wasted money, and the contribution charge is coming either way. Many rural areas have no plan at all, in which case the jokaso is permanent.
| Japanese | English |
|---|---|
| 浄化槽は合併処理ですか、単独処理ですか。人槽と設置年を教えてください。 | Is the tank combined or single treatment? Capacity in persons and year installed? |
| 直近の法定検査結果書と、保守点検・清掃の契約書を見せてください。 | Please show the latest statutory inspection certificate and the maintenance/cleaning contracts. |
| ブロワーは動いていますか。最後に清掃したのはいつですか。 | Is the blower running? When was it last pumped? |
| この地区に下水道の整備計画はありますか。受益者負担金は発生しますか。 | Is there a sewer plan for this area? Will a beneficiary contribution be charged? |
| 浄化槽の入れ替えに市の補助金はありますか。 | Does the town subsidise tank replacement? |
A well-maintained combined tank is a neutral item: it costs about what a sewer would and needs a contractor on call. A single-treatment tank or a vault toilet is a genuine cost line — put ¥1,000,000–1,500,000 in the renovation budget, then check the subsidy. A tank of unknown condition on a house empty for a decade is a risk item until a contractor has looked at it, which they will usually do for a small fee before purchase.
Akiya Check reports mark the drainage type from the listing text and rate a single-treatment tank or vault toilet as CAUTION, with these questions attached. If the listing does not state the drainage type, the report marks it UNKNOWN rather than guessing.
No. Outside city centres it is the norm. The questions are whether it is a combined tank, whether it has been maintained, and whether a sewer is planned. Each of those is a cost you can put a number on.
The statutory inspection must be done by the designated body, and the clean-out by a licensed contractor with a vacuum truck. Maintenance visits are also expected to be done by a registered contractor; owners can add disinfectant and check the blower between visits but cannot replace the contract.
A working tank with a running blower should not. Odour usually means the blower has stopped, the tank is overdue for pumping, or the vent is blocked — all cheap to fix. Persistent smell on an unused akiya is a sign the tank needs a restart service.
Most municipalities with no sewer plan subsidise replacing single-treatment tanks or vault toilets with combined tanks, often several hundred thousand yen. Conditions typically include being the resident owner and applying before work starts. Confirm with the town's environment or water division.
Capacity is set by floor area under the building code standard (roughly 5 persons for a house under about 130 m², 7 persons above), not by the number of occupants. A larger tank costs more to pump but is not a problem in itself.
Have a specific listing in mind? Get the official zoning, hazard and transaction data for that exact lot — plus the questions to send the agent — in one PDF.
Get a $49 risk report Free 12-point checklistThis guide is general information based on public sources cited above. It is not legal, tax, or real-estate brokerage advice. Confirm every item for a specific property with the agent, the municipality, and licensed professionals.