How do I disable network printer discovery in Ubuntu 17.10?

You need to disable Bonjour on your printer.

Assuming the web interface for the HP 8500 is similar to the HP 8740, do the following:

1. In your web browser, go to your printer's setting page.

   https://nnn.nnn.nnn.nnn/

   Replace nnn.nnn.nnn.nnn with the IP address of your printer. (For local addresses, it is always a good idea to put the "/" at the end of the address).

   If you get a warning, "Your connection is not private", then click "Advanced" and select the "Proceed to ..." link. (This is for Chrome, so the message on other web browsers may differ slightly).

   You will be taken to the printer's web configuration page.

2. Click on Network

3. Click + Advanced Settings to expand it

4. Click Bonjour

5. Select the Disable Bonjour radio button

6. Click the Apply button

7. The duplicate network detected printer should disappear from your Ubuntu system. If you manually setup the printer (using hplip), that version of the printer will still be available on your system.