Inject, brine or both for fried turkey?

skid you can do both. i find best is to brine it 2 days ahead of time for 24 hours. then remove from brine pat dry and inject and season skin with tony's or ur favorite cajun seasoning and rub down with french's yellow mustard. wrap tightly with saran wrap and refrigerate for 24 hours. pull it out of fridge about 2 hours before you fry so it will cook evenly. then fry. done this the past 3 years and never had any complaints. its a lot of work though.

2nd question:
yes you CAN still use the oil after. this all depends on the temp that you cooked your turkey in. if your temp is too high then you'll burn the grease as well as any bits that fall off the turkey and it will make everything you fry in it taste like shite. that being considered, id let it cool and strain it through some cheese cloth or a coffee filter if it doesnt appear to be burnt. this is messy but peanut oil is expensive.