You don’t have to hook the pressure line from the muffler to the tank. We flew many years with the tank simply vented to the atmosphere. If you don’t connect the line, the engine will be quite lean and you must richen the needle valve a good bit to get it running right. By connecting the pressure line to the tank, you get better fuel draw during abrupt aerobatic maneuvers. With a trainer it won’t make much difference. If you choose to do it, the pressure line from the muffler is connected directly to the tank vent.