Septic tank for alternative sewer systems

In a corrugated sewage tank which has a bottom wall and generally vertically extending alternating ribs and valleys which define a corrugated side wall extending between the bottom wall and an apex area and which bottom wall tends to flex inward and which ribs and valleys tend to compress in an accordion-like manner under large pressure differentials between the tank interior and exterior, the improvement comprising:

• a bottom area reinforcing means for increasing resistance to inward flexation of the bottom wall and compression of the side wall valleys and ribs adjacent the bottom wall, the bottom area reinforcing means including an inwardly domed bottom wall, and a plurality of downward projections for preventing fluid in the interior of the tank from flexing the bottom wall outward.

In a generally spherical round, plastic tank which has an access aperture in an apex area of the tank and a riser extending upward from the apex area and around the access aperture, the improvement comprising:

• an apex area reinforcing means for increasing resistance of the apex area adjacent the access aperture to becoming distorted under exterior hydrostatic pressure when the tank is at least partially immersed in water-laden soil, the apex area reinforcing means including an outward projection which projects generally perpendicular to the tank apex area and extends annularly around and displaced from the riser to inhibit distortion of the apex area.

In a corrugated plastic sewage tank which has a bottom wall, an apex area, and a side wall defined by generally vertical alternating ribs and valleys, which bottom wall and apex area tend to flex inward and which ribs and valleys tend to compress in an accordion-like manner under a large pressure differential between the tank interior and exterior, the improvement comprising:

• a reinforcing means for increasing resistance to inward flexation of at least one of the bottom wall and the apex area which increases resistance to compression of the valley and ribs thereadjacent, reinforcing means including at least one rigid reinforcing ring which is attached to the tank adjacent one of the tank bottom wall and the apex area to constrain it against inward flexation such that the side wall ribs and valleys are held in an uncompressed configuration, such that loss of side wall strength attributable to the accordion-like compressing of the ribs and valleys is prevented.

In a corrugated plastic sewage tank which has bottom wall and a side wall defined by generally vertical alternating ribs and valleys, which bottom wall tends to flex inward and which ribs and valleys tend to compress in an accordion-like manner under a large pressure differential between the tank interior and exterior, the improvement comprising:

• an inwardly doomed bottom wall portion;
• and,
• a plurality of downward projecting structures extending from the domed bottom wall portion generally to a horizontal plane across a bottom of the tank to inhibit outward deflection of the domed bottom wall.

In a corrugated plastic sewage tank which has a side wall defined by generally vertical alternating ribs and valleys extending between a bottom wall and an apex area, an access opening protecting riser extending upward from the apex area, the apex area tending to become distorted under exterior hydrostatic pressure when the tank is disposed in water-laden soil which distortion permits the ribs and valleys to compress in an accordion-like manner reducing their structural strength permitting the tank to collapse, the improvement comprising:

• a rigid, annular structure mounted to the tank apex area spaced from and extending peripherally around the riser, the annular structure having sufficient rigidity to inhibit the apex area from becoming distorted under the water-laden soil exterior hydrostatic pressure to prevent the ribs and valleys from compressing in the accordion-like manner such that the tank retains its structural strength under the water-laden soil exterior hydrostatic pressure, whereby the annular structure increases the rigidity of the apex area sufficiently for the tank to retain its shape and structural strength.

The corrugated plastic tank for subterranean installation, the tank comprising:

• a corrugated side wall which extends from a bottom wall area to an apex area;
• an opening defined through the side wall for receiving a generally horizontally extending section of tubing;
• at least one corrugation defined in the side wall extending annularly around the opening to permit a side wall portion defined between the corrugation and the opening to move relative to the remainder of the side wall as the tubing length moves.