A three line tank is required with the 10,15 and 20 cc Evo's that require tank pressure because if a tee is used for a two line tank system, gas will leak from the carb during filling and perhaps more of an issue, is that the tank can't be be drained. If there is a new pumped carb for the 15 and 20, that eliminates the need for tank pressure, a Tee might work. The instructions with such a system should detail the answer.