I'm not really clear as to what you are trying to do. You don't want to inventory cleaning cartridges - it wastes them.
The slot you want to be your cleaning cartridge needs to be configured as a cleaning slot. From the devices tab, expand Robotic Libraries down to slots. When you click slots, they should all show up in the upper right window. Right click that slot and go to properties. There is a check box in there that needs to be clicked to make sure that BE knows it is a cleaning tape in there.
Also, if you are setting up like this, the Autoclean feature on the library should be disabled.
If I am way off base here, drop a reply and we'll try to help further.