Gray tank flush valve replacement anyone ever done this ?

 just got the parts from the factory, a small 1/2" silver oval handle twist ball valve. The original ball valve had a black handle that was leaking and I can not seem to get a bite on the screw head where it is leaking. Looks like I need to cut off the 1/2" crimp rings that hold the Plex rings on and re-crimp, I also need to replace the toggle switch for the macerator as the connections on the back side of that switch are really rusted and corroded anyone ever do a repair like this and what is the best way to clean a connection that is badly corroded

Sometimes connections like that are just fine.  They may look corroded on the surface but the metal to metal contact might be OK.  If it was me I would carefully unscrew those terminals, wire brush everything shiny and coat the metal with di-electric grease and re-connect.  The di-electric helps keep water from corroding the metal in the future.  You might need to re-apply every couple of years. 

I would also keep a spare toggle on hand it case it fails but not sure I would worry about replacing it if it still works.

I also need to replace the toggle switch for the macerator as the connections on the back side of that switch are really rusted and corroded anyone ever do a repair like this and what is the best way to clean a connection that is badly corroded

I would not bother trying to save those ring connectors, as water has progressed inside the insulation of the wire also. (Educated guess there... but I will put money on it.  )

Remove the retaining nut(s) that hold the switch on, then cut both wires right next to the connector crimp end. Strip the wires for a new connector, but INSPECT first - is the copper nice and shiny? Then put some dielectric grease (or Vaseline if no dielectric), crimp on the connectors and proceed with switch replacement.

If the wire inside is black, or worse yet green and flaky... keep cutting the wire back until you reach nice shiny wire. Then proceed with connector, dielectric and replacement of switch. Little bit of shrink tubing Squishing out the dielectric as it seals for the 'gold star' on your report card. 

There are ways to chemically clean the wire back to shiny, but they do not address the wire hidden in the insulation. That would be a 'half fast'  repair in my book.

You can certainly just clean off the ring connector and connect to the new switch,  but the lack of sealing (shrink tubing) on the crimp connection and the age of the connection would have me doing more investigating while down there. But that's one of my quirks.. I only like going in once to fix something. 

I imagine the corrosion is many inches inside the wire insulation.

I believe in "soldering".  It's more work, but worth it.  I advise to cut off the old crimped-on ring terminal with yellow plastic, strip off a 1/2 inch of insulation and clean up the end of the stranded wire with fine steel wool until it's all shinny copper.  Then thread it into a new rig terminal with no yellow plastic on it.  The plastic will only hold water.  Don't crimp the connection, solder it.  Then grease it all up just prior to attachment onto the switch.

I imagine the corrosion is many inches inside the wire insulation.

I believe in "soldering".  It's more work, but worth it.  I advise to cut off the old crimped-on ring terminal with yellow plastic, strip off a 1/2 inch of insulation and clean up the end of the stranded wire with fine steel wool until it's all shinny copper.  Then thread it into a new rig terminal with no yellow plastic on it.  The plastic will only hold water.  Don't crimp the connection, solder it.  Then grease it all up just prior to attachment onto the switch.

I was also a 'solder all the time when possible'  advocate, coming from 'circuit board electronics' in my youth... but after testing and education, I have been won over to 'crimp and seal'.  Just like...um...every vehicle manufacturer I can think of.     For applications with vibration, it has been shown to be superior, with no work hardening from vibration like happens at the tinned/untinned junction in the wire. EG: https://www.hpacademy.com/technical-articles/solder-vs-crimping/

The long method - use dielectric inside, heat shrink outside. The quickie - self sealing crimp connectors, here's one brand - http://phillipsind.com/main/wire-terminals/sta-dry-crimp-seal-heat-shrink-terminals/sta-dry-crimp-ring-terminals.html    We have the Kimball Midwest version, and they rock.

Thank you so much for the great advice. The job is done and I will post some pictures of the work as soon as the rain stops. I got some help from a local RV repair tech who helped me get er done we replaced both flush ball valves and the toggle switch .. thanks again