Left fish tank outside for a month, can i put fish back in or will they die because of bactreria?

my fishtank has been outside without fish for a month, i want to put it back in the house with the fish. my fish have currently been living in a small bucket....can i move the fish inside the tank immediately or do i have to wait a week for the bacteria to grow so they dont die?. i left the original filter in the tank too. and how should i clean the tank?...its pretty nasty, it has orange mildew on everything including the gravel.