Buying a house with a septic system: what to check

A septic system is one of the most expensive parts of a house to repair or replace, and most of it is buried where you can’t see it. A few documents and a proper inspection before closing tell you what you are buying.

Start with the paperwork

Ask the seller or the listing agent for these, and request what is missing from the county or town health department:

• The septic permit and the “as-built” drawing. The EPA’s septic FAQ says your local health department usually keeps the permit and the design, which show where the tank and drain field are and when the system was installed.
• Pumping and service records. Dates of past pumpings, the sludge and scum measurements and any repairs.
• A history of problems. The Connecticut Department of Public Health suggests asking the seller directly whether the system has ever shown signs of failure.

Connecticut’s guide also suggests talking with the local sanitarian (the health department’s septic official) about common repairs and how long systems tend to last in that neighborhood. If the seller has no records at all, treat the system’s condition as unknown until it is inspected.

Get a professional septic inspection

The EPA advises having the system inspected by a septic system service provider before you buy, and notes that inspections may be required by your local or state government or your mortgage lender. A standard home inspection may not open the tank, so bring in a septic professional for this part.

According to the EPA’s homebuyer guide, the inspector should check:

Connecticut’s guide adds two useful points. Opening the tank is the most reliable check, while a dye test only catches a system that has failed badly. And timing matters: a system tested in dry summer weather can look fine and then sit in high groundwater in spring. Ask the inspector how they will test, and whether they will dig to reach the lids.

Compare the tank size with the house

Septic systems are designed around the number of bedrooms, because bedrooms set how many people are likely to live there. Rules differ by state and county, but as one example, the University of Nebraska-Lincoln’s water program says the minimum tank there is 1,000 gallons for a three-bedroom house and 1,250 gallons for four bedrooms.

Check the permit for the tank size and the number of bedrooms it was approved for. Watch for:

• A house that has been expanded (a finished basement or an added bedroom) without a matching septic upgrade.
• A household larger than the one before you. Connecticut notes that a system can be undersized for a family that uses much more water than the previous owners.

Find the drain field and look at it

The drain field is where the liquid from the tank soaks into the soil, and it is the costliest part to replace. Use the as-built drawing or ask the inspector to locate it, then walk over it yourself. The EPA lists these warning signs of a failing system:

• Wastewater backing up or gurgling in the drains.
• A strong odor around the tank or the drain field.
• Bright green, spongy grass over the drain field, even in dry weather.
• Standing water, damp spots or soft, wet soil when it hasn’t rained much.

Also notice anything that can damage the field: a driveway, a shed or parking area over it, or trees planted close by. The EPA’s septic care guide says vehicles compact the soil and can damage the pipes, and tree roots can clog the field. Our guide to drain field basics explains how it works.

Never open a septic tank and lean in, and never climb inside one. Oregon State University Extension warns that the gases in a tank can kill a person very quickly. Let the septic professional handle the lids.

Red flags that call for a second look

Talk with your agent before you go further if the inspection finds any of these:

• Sewage surfacing in the yard or backing up into the house.
• A cracked tank, broken baffles or pipes, or signs of past backups.
• No permit on file, or a system that doesn’t match the permit.
• A tank that has not been pumped in many years with no records.

A problem doesn’t always mean you should walk away. The inspection report gives you facts to negotiate repairs, a credit or a price change, or to budget for the work. For typical costs, see our guide to septic tank pumping cost.

After you move in

Start your own records on day one:

1. Keep the inspection report and the as-built drawing together.
2. If the inspector found the tank close to full, have it pumped soon.
3. Plan on pumping every 3 to 5 years and an inspection at least every 3 years, as the EPA recommends.
4. Flush only human waste and toilet paper, and limit the garbage disposal.

If you are new to septic, our guide on how a septic system works is a good next read.