Methods and systems are provided for an adaptor for a capless filler pipe of a fuel tank for leak detection testing of a vehicle. In one example, the system may include a threaded hollow shaft having a top end able to receive a nozzle of a leak detection machine, the hollow shaft inserted through a mouth of a filler pipe of a fuel tank, a gasket arranged on the hollow shaft, and an end cylinder having an elastic piece on the hollow shaft configured to create an airtight seal with the fuel mouth. In this way, the adaptor may restrict gas flow through a defined flow path through the adaptor, and not through any other flow paths during leak detection testing.