I used to brine pork and had good results, but it was cumbersome.
Then I started injecting which made the task easier and less clean up. I used Chris Lilly's Injection but found it too be salty to my tastes, I cut back to almost half the amount of salt and it is still good. Several years ago I switched to OakRidge Game Changer Brine as my Injection and have nothing less than great results with it. The main reason for brining a pork butt isn't to add moisture because the pork butt has enough fat and connective tissue to retain moisture.
The main reason I brine is for added flavors deep into the meat, added tenderness and added moisture are just an added byproduct of brining, as well as an improved texture.
I now, always use OakRidge Game Changer Brine as an injection. I Use fruit juice (Peach, Pear, Apple, or White Grape) for added flavors. For every 8 ounces of juice add 1 Tablespoon of OakRidge Game Changer Brine and then inject into the pork. I inject right through the cyro-packaging to save with cleanup, using different angles through the same hole to prevent leaking. I used to rub and let the pork sit overnight, but now I'll rub a few hours before smoking depending upon my time constraints.
When cooking injected pork butts I find the bone begins to wiggle at about 187°, I pull and rest the pork in a cambro/cooler for 3 to 4 hours, and pull the pork just before serving. I find the OakRidge Game Changer Brine keeps the pork exceptionally tender, moist, very flavorful, and it pulls in very long strands which is pleasing to the eyes and great for building big sandwiches.