Look how to remove old leaking drain and install the new tub pipe.
Never use silicone in this place. That's why this is not a silicone. This is a special waterproof sealer, works even underwater and stay soft and sticky to surface after years. It's much better than drying out plumbers putty, which can cracks and lost surface contact.
Home repair, do it yourself, how to, plumbing trick,
как удалить старый подтекающий слив, установить новую трубу ванны