They are light to handle, and quite durable, but they have been known to break due to shifting ground and are hard to repair. Manufacturers claim an estimated life span of 30 years. They are usually precast and are the best and most common type of tanks. The tank may not be properly sealed and small leaks can grow larger. Leaks can be fixed, but the tank must be properly cleaned and prepared, and techniques are difficult and dangerous in an older tank.
All tanks can leak around the inlet and outlet connections.
This can usually be repaired by re-sealing the joints with caulk or mortar. Due to accumulation of gases, concrete outlet connections often disintegrate. Old ones should be replaced with plastic fittings. Any underground tank that has had sewage in it is dangerous due to gases, especially if you are working alone. Only a trained professional with a self-contained breathing apparatus should enter a septic tank.