Help w/ Clean Install of Win 10....Wish to wipe hard drive clean before selling old machine...

you can use Windows installation media USB or DVD to boot the old PC, choose Custom Install (advanced), then delete all partitions on the drives.  when that is done power off do not proceed to install anything

this does not truly wipe drive but for most ordinary people it is good enough.

if you want a thorough deep wipe, try DBAND on a bootable small 1-2 GB USB flash drive.  DBAND only works on HDD and not ssd.  It can take a couple of hours to wipe a large HDD

https://dban.org/

Review this article, then go to BIOS setup to see if your system has Dell Data Wipe feature.  It's a simple process with the built-in tool.  https://www.dell.com/support/kbdoc/en-us/000146892/dell-data-wipe

Create a Windows 10 installer from Microsoft Windows Creation Tool.  Perform Windows installation to you old system.  At the select keyboard region and other settings, force shutdown and let new owner to complete the OOBE (out of the box experience). 

good Dell link from chino, in there you may also find

https://www.dell.com/support/kbdoc/en-us/000192008/how-do-i-erase-data-from-my-hard-drive-or-mobile-device-before-trade-in

Windows 11 or Windows 10 Reset

1. Click Start , then type reset.
2. Select Reset this personal computer (System Setting).
3. Under Reset this personal computer, select Get Started.
4. Select the option to Remove everything to remove all your personal files, apps, and settings.
5. Select Remove files and clean the drive.
6. Review the information about the page, and click Reset to proceed further.
7. Follow the on-screen instructions to complete the reset process. This takes some time and your computer restart. Depending on the type, size of disks, and configuration of the system, the process can take from an hour to a few hours.

https://www.dell.com/support/kbdoc/en-us/000150908/data-removal-processes-for-a-solid-state-hard-drive