Well theres a few ways of shuttin it . yes it has to be a tight seal so the first way is to simply use an actuator with the adjuster rod wound in all the way so its tight and dont connect the vac pipe , therefore it will just act as a stopper . second is to use a piece of threaded bar to again hold the flap shut tigh . and the third is to weld it shut thus being able to remove all trace of the internal gate bar the penny flap which MUST stay in and remain tightly shut . Cheers Ally