Rooto Corp. 1185 Root Killer 2 lb

How much do i need to get started, and how often do i need to use it?

Can I pour this down my outside patio drain and push it through with some hose water?

Can you put in septic tank clean out

Could this kill The rest of the sissoo tree we cut down and it’s invasive roots? I don’t have a problem with pipes but need these things gone.