cleaning fixer bottle

Today I poured away the exhausted fixer. It remained a dark grey coating on the bottle wall (silver?) which I could not totally get rid of by washing and shaking the bottle with cold and hot water. Is it necessary to remove this coating before I fill the bottle with fresh fixer? And if so, how can I bring it about?

It's best to clean with a solution of Potassiun Ferricyanide/Potassium bromide, bleach the silver then dissolve it with the old fixer, before washing and re-using.

Leaving it means adding unnecessary silver content to the fresh fixer.

Ian