Russ, we are not using any boiler compound in our loco's. We do have soft water though and that makes any hot drink tasty. My saying is this: "If you can't drink it, why put it in your boiler!"
Of course I know that some places in this country the water is terrible and you need to treat. The best valve to use in making trycock cocoa and any other warm beverage would be the lower trycock, however the deck hose works well too! And if you wanted to get creative, your blowdown on the water glass could work.
Ahhh note to self. When making warm beverage next time, make sure deck hose valve is off so oil can doesn't get old facefull!
When you were there the day before, we had a rough startup and some personality clashes which is why we did not get any backhead time. However, after more angioplasty at freeze-thirty in the morning we got her hot in no time and began the day right...with breakfast!