The correct answer is C) loss of suction. When stripping a tank, excessive air in the suction line can cause a loss of suction. This is because the air in the suction line reduces the ability of the pump to draw liquid from the tank, leading to a loss of suction and decreased pump performance. The other options are incorrect because: A) An over pressurized line is not caused by excessive air in the suction line, but rather by a blockage or restriction in the discharge line. B) Back pressure is not a direct result of excessive air in the suction line, but rather a consequence of a restriction or obstruction in the discharge system. D) An increase in suction is the opposite of what would occur with excessive air in the suction line, which would lead to a loss of suction.