Concrete, Polyethylene, or Fiberglass: Choosing a Septic Tank

Published July 1, 2026

Once you know you need a new tank, the next question is what it should be made of. The three common choices, concrete, polyethylene, and fiberglass, all hold wastewater and all pass inspection when installed right, but they behave differently in Maine ground. Here is how to think through the decision before you commit to a tank you will keep for thirty years or more.

Concrete: The Heavy, Traditional Choice

Concrete is still the default across Penobscot County, and for good reason. A concrete tank is heavy enough that it will not float in a high water table, and a well cast unit lasts for decades. The tradeoffs are weight and cracking. It takes machinery to set a concrete tank, so access to the install spot matters, and older or poorly cast tanks can crack and leak over time. For most standard lots with room to work, concrete is a dependable pick.

Polyethylene: Light and Seamless

Polyethylene (HDPE) tanks are molded in one piece, so there are no seams to leak, and they are light enough to place on lots where a concrete truck and boom cannot reach. That makes them a strong fit for tight or wooded parcels. The catch is buoyancy. A plastic tank can float if the water table is high and the tank is not properly ballasted, so the install has to account for it. Done right, a poly tank is a clean, corrosion proof option.

Fiberglass: Corrosion Proof in Wet Ground

Fiberglass (FRP) tanks split the difference. They resist the corrosion that can attack concrete in acidic or wet soil, they are lighter than concrete, and they are strong. They tend to cost more than the other two, and like polyethylene they need proper anchoring where groundwater is high. For a wet lot where you want long corrosion resistance, fiberglass earns its price.

Match the Tank to Your Lot

There is no single best material, only the best material for your soil, your access, and your budget. A dry lot with good access near the Broadway Historic District might be an easy concrete job, while a wet, wooded parcel out toward Holden could call for poly or fiberglass with anchoring. The perc test and site evaluation tell us which way to lean before you spend a dollar. You can read more on our new septic system installation page, or contact us with the details of your lot.

Thinking about a new tank for your Bangor property? Call Bookjs at (207) 556-6455 for a free site evaluation and a straight recommendation.