You can not really clear slice 5. Slice 5 is just a region on the disk starting at 36640 and ending at 40510.

It depends on what you want to do with slice 5.

* If you need another file system: umount fs, run newfs, mount fs again

* If you want the slice to not hold information: run newfs , do not mount the file system, or ...

* Set the start and end of the slice to 40000 (or any other address with the 36641-40509 range)

* Merge with other slices: can only be done with slice 4 and 6 and will result in loss of data in slice 4, 5 and 6
Umount file systems in slice 4, 5 and 6
Backup file systems
Set begin and end of slice 5 to 0
Set begin and end of slice 6 to 0
Set begin of slice 4 to 32769 and end of slice to 50831
newfs slice4
mount new fs
(maybe) restore backup of slice 4, 5 and 6 to new file system in slice 4