boiling water on utensils in "non-kosher" sink

Kashrut
1

we recently moved into an apartment with previously non-jewish tenants. A kosher knife was sitting in the sink and boiling hot water was poured into the sink.

1.if a sink will have boiling hot water poured into it should it be kashered?
2. does the knife need to be kashered?
3. the boiling hot water was from gefilte fish and the knife is used with meat should it be kashered?

Thank you

2
  1. No need
  2. No
  3. No need