Go find a 5 gallon bucket with a lid, preferably food grade. Wash and sanitize it.
If your turkey is much larger than 20lbs than it might not fit in a 5-gallon bucket whole. You have two choices here, you can find a bigger container like a plastic tote or cooler you can piece the turkey up and try and fit it into a 5-gallon bucket.
Let’s assume it fits into the bucket
Mix half of the brine solution and dump the brine into the bucket.
Put the turkey into the bucket neck first.
Mix the other half of the brine in a large pitcher or bowl and dump onto the turkey in the bucket.
Depending upon the size of your turkey you might have to make another half batch of the brine and dump it into the bucket to cover the turkey.
Once the turkey is covered put a lid on the bucket and place the bucket somewhere close to fridge temperture.
Brine for 24-48 hours and then remove.