NY guide lines for private house

[Meng W.]

Hi BP members, I own a house and I understand I have to provide necessary services to the house and tenants. However, let's say a tenant has a toilet leaking under the tank or a clogged toilet, is it the duty of the landlord to provide that service or can the tenant hire an outside job to do so. I know it sounds a bit stupid, but just curious. 

Also one last thing if a tenant decides to hire an outside locksmith to replace all the doorknobs to each room is it legal for them to do so? The lease states any changes must be confirmed with landlord. However the tenant's lease expired three years ago, does it still pertain to them? 

Thank you for time and patience BP members.