What tool is needed to remove KMC X11 w/MissingLink, 11-speed chain? I need to take it out and then clean it- its full of sand. Maybe even replace it. Does any universal chain tool work. Should I get one from the manufacturer.
Any tool that can be used on an 11-speed chain should work to 'break-the-link', i.e. push the pin (rivet) out.  I have never updated my Park CT-3 tool in years and have used it on a variety of chain variations, from 8 speed up to 11.

You should look for a KMC replacement master link, as most manufacturers do not recommend using other manufacturer's master links.

I'm not a huge fan of pushing pins back in place, but if you have the right tool, it is doable, the simplicity of the self-locking master links makes reconnecting the chain way easier--I carry both 10- and 11- speed links with my, never know when you might need one, or can help someone out, they are light and cheap enough.

I personally have the KMC Connector and Removal tools, I really like the connector tool, as the 'stomp-on-the-pedal' method seems sketchy, imo.