I want to brine a turkey but have heard conflicting messages on how much salt to use. I have heard 5% salt mixture and from others I have heard 10 salt mixture. I would like a somewhat strong taste of salt. For the sake of this question we can assume I'm going to use 5 litres of water.
A good turkey brine should be around a 9% solution - 9g salt per 100g water - that's 90g salt per liter. You shouldn't go below 6% brine, but using a solution anywhere in the range of 6% - 9% should give you excellent results. Soak for 12 hours if you're soaking a whole bird - keep it to around 6 hours if you're brining just the breast. Be sure to rinse the bird after brining to wash-away excess surface salt.
FYI - The drippings from the turkey will be extremely salty - they probably won't be suitable for making gravy.
You might want to explore "equilibrium brining." While a bit slower, it makes it very difficult to over-brine and have a product that is too salty. See this link for details: http://www.chefsteps.com/activities/equilibrium-brining