How do you get past the guard in lavender town in silver

you catch a level 20 Gastly or higher then play poke flute and make sure you get all the items from the market basement probably in goldenrod town have the ghost pokemon with you. I also I think you have to have Gengar, Hunter also. there will be a pokemon at the top of the tower use poke flute to knock it out. I don't think you could catch them.