Do printers and scanners really save every single document?

I have some old printers and scanners that I'd like to donate or sell

I've read news articles that claim that printers and scanners store all of the documents that pass through them. Is this true?

Or are these claims exaggerated?

Is there a way to securely wipe the data on these devices?

I have a wifi-enabled printer. Would this printer retain info on my wifi network and password after I press the "forget network" button?

articles claim claims data document documents donate old pass printers privacy scanners sell single store wipe