Abstract: A sewage tank comprising an outer shell of plywood which includes a platform for supporting a toilet pan. An inner lining of a compressible plastic material lines the interior of the outer shell and defines a hollow interior region of variable volume for a bladder for storing sewage. The inner lining accommodates expansion and contraction of the bladder in the event of freezing and thawing of the contents thereof. The contents of the toilet pan are discharged into the bladder, and sewage is discharged from the bladder under pressure through a discharge pipe.