How to make a bootable USB drive from Install OS X El Capitan.app? I wish to upgrade from Snow Leopard (10.6.8) to anything higher.

Disk Utilities repair says the disk needs to be repaired.  So, I need to boot onto something other than the boot drive to run disk utilities.

I downloaded El Capitan from the App Store.  It appears to be an install app.  I tried diskmakerx, but it requires 10.7 or higher.  Not sure how to make a bootable image from the install app in Applications.

I can't use OS X Recovery, that also requires 10.7 or higher.

These directions require the DVD media, which my parents likely never had.

All the directions I've found for bootable USBs require a disk image.

Any options?

Edit 1: I created a USB drive using these directions, "Option 2: Use Disk Utility."  I modified a bit (El Capitan instead of Yosemite, got the BaseImage.dmg by copying and using xattr to remove the invisible bit, ..), but I have a USB key with "Mac OS Extended" format and 7.8G of stuff on it.

When I boot up holding down the option key, it doesn't show any menu to choose where to boot from, it just ignores my USB drive.  When I open the "Startup Disk" system preferences dialog, it does not show the USB drive (even though it is mounted).  It is plugged directly into this mac mini, not through a hub or keyboard.

I looked around for related questions (e.g., here), and found nothing relevant.

Any idea of how to debug a USB drive being ignored upon (Snow Leopard) startup?
(From OS X Daily)

You'll need an 8 GB or larger USB Drive. Remember, it will be erased, so backup any important files.

Use the following command in Terminal (assuming the Install OS X El Capitan app is in /Applications, which where the App Store installs it by default)

Also make note of the USB Volume Label and use its name in the command below in place of: &lt;USB_Volume_Name&gt;

sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume "/Volumes/&lt;USB_Volume_Name&gt;" --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app --nointeraction