What’s better, a metal or concrete septic tank?

What is better, a metal or a concrete septic or holding tank?—Grant Gibson, via e-mail

Metal rusts and becomes perforated and, eventually, a metal tank can collapse. Not so with concrete. Sure, you’ll find both 40-year-old metal tanks and 40-year-old concrete tanks in cottage country, but the metal ones are probably in worse shape. Concrete wins! Also, if you’re asking because you’re planning to install a new tank (and not, say, because you’re trying to settle a bet with your neighbour), it would be tough to find anybody selling metal tanks these days.

Even though the Ontario Building Code doesn’t specifically prohibit metal tanks, all new tanks must meet certain standards, and it’s very hard to comply with metal, says James Ross of the Ministry of Municipal Affairs and Housing.

You didn’t ask about plastic, but it’s possibly a better option than concrete, depending on your circumstances. Doug Schultz, the chief building official for the Township of Whitewater Region, recommends plastic if there’s a high salt content in your water or if you use a water softener (the salt may cause concrete to break down). Also, plastic is lighter, so it’s usually easier to install.

Points go to concrete, though, for having proven its longevity. “It’s survived the test of time,” says Bill Goodale, a consulting engineer with CC Tatham and Associates who does septic inspections for the Township of Tiny. “Plastic tanks haven’t been around for forty years.”