yup 118g was what i got
calculated the area of a square of 37"
then calculated the area of the isosceles right triangle of 10.83"
then (area of square) - 4(area of triangle) = area of octagon
then (area of octagon)*height = volume of the tank
hope this helps
or
there are 8 triangles of height 18.5" and base 15.3"
so area of triangle is 141.5sq.inches
and then 8*area of triangle*height of tank=volume