Adjective clauses

Does anyone know a rule for when we use when/that/which in adjective clasuses in the objective case?

Sometimes you can use either

I remember the day when I met him

I remember the day that I met him

Sometimes only one seems to work

June is the month in which we have a lot of rain

It was a great summer that I'll never forget (we can't use when)

When we get together, we like to talk about the old days when we all lived at home (we can't use which or that)