I feel so strongly about this issue that I must break my lurking silence. Plain old gaffer tape (I'm referring to the tape being plain and old, not the gaffer - just in case there are any gaffers reading this) really will not do in a proper darkroom. You must get genuine Leica black tape from a Leica dealer. This stuff effectively covers anything red and it sticks to everything, including silk-embroidered newt skin with hammertone finish.
'Hope this helps.'