would wiping out my hard drive delete the OS?

Solution
That process is called Formatting the drive

Download & install: Piriform CCleaner
Go to; Tools>Drive Wiper>Select the Dive>Where it says "Wipe".Select "Entire Drive">Wipe>Done
Overwrites by default, meaning data cannot be recovered or 'un-deleted'. Safe to give away for someone else to use with your own data permanently gone
That process is called Formatting the drive

Download & install: Piriform CCleaner
Go to; Tools>Drive Wiper>Select the Dive>Where it says "Wipe".Select "Entire Drive">Wipe>Done
Overwrites by default, meaning data cannot be recovered or 'un-deleted'. Safe to give away for someone else to use with your own data permanently gone
 
Solution
It has a 1/3/7/35 Pass overwrite option, 3 pass by default but 1 pass is enough, the more 'passes' the longer it takes too.
1 pass is most often always enough though

Personally i use CCleaner alot as a 'disk cleaner' / junk/history cleaner but reserve a program on bootable usb disk to wipe physical disks which i would connect through a hot swappable caddy/enclosure
 


yeah me to never really a full wipe just for junk.