Preston
That sounds right the gray is usually 1 1/2 and the black is 3"
You can a easily find both at any good RV parts shop or online at Amazon remember to get the kits with the flange bolts as the bolts tend to get rusty and can break getting it apart.
also make sure to get the valves with the handle threaded on as some are just a molded on handle and you will need the threads for your application.
This video should help you familiarize your self with the system.
https://youtu.be/gL7hJKgFyNI?si=sZ8b82F3KWLae_4xEric