There really is no reason to physically erase a tape for reuse since running a backup operation set to "Overwrite" mode effectively erases any previous data that may have existed on the tape being used. Additionally, erasing a tape puts unnecessary wear on both the tape being erased and the tape drive, thereby shortening the lifespan of both the tape and the drive. Therefore, if your only reason for erasing a tape is to allow new data to be written, this is an unnecessary step and can lead to unexpected data loss if the wrong tape is mistakenly erased.
When performing an overwrite of a tape with BRU Server, BRU LE or BRU PE, the archive(s) on the tape is automatically deleted from the BRU archive database and therefore no manual cleanup is required.
The only real time that you would need to erase a tape, which can take several hours, is if you are permanently retiring or destroying the media. In that case, physical destruction of the tape is the only truly secure method for protecting any data that may have been previously written to the tape.
If you absolutely must erase a tape, you can do so from the command line with the appropriate tape management tool for your system - tapectl (for BRU installations on Mac OS X), mt (Linux/Unix), etc. Refer to that tool's documentation for specifics on erasing tapes.