I have struggled with an easy way to drain the liquid off of a can of tuna. Usually I just use the lid of the tin to press the liquid out, but it rarely gets it dry enough for my taste. I searched everywhere to find something more efficient, but it was right in my utensil drawer all along! Its a metal lemon squeezer! I just put the contents of the can in the inside part of the squeezer, press the top part of the handle down and squeeze until it's as dry as I want it. You may have to stop to push some of the tuna back in that comes out around the edges, but it works great.
There is a little device, sort of like the garlic press, made especially for draining canned tuna. It fits right over the opening, push handle down and fully drained to your liking.