Transmission dipstick will not stop leaking

Can I get a yes or no shouldn't I be able to use a boat drain plug to put in place of my fill tube on my transmission to stop it from leaking I feel that that would be a good fix once I know I have the right amount of fluid in cuz I just cannot get the fill tube to seal and I'm tired of wasting transmission fluid it's expensive
and yes I did put a 5.7 l vortec in it runs perfect