This is the combination and amounts of ingredients that I have found works for me and is a hit when I put it into tuna sandwiches. The trick is not to let it get soupy. Got to watch the mayo and the relish.
Peel and chop the boiled eggs. I chop eggs by hand as there is too much wasted egg chopping them in processor. Set aside.
In a mixing bowl, place drained tuna, chopped egg, pickle relish, chopped celery and chopped onion.I learned the hard way not to use food process on the tuna at all.
Gently mix all ingredients except mayonnaise into the well drained tuna until all are intermixed.
Adding the mayonnaise: The secret to the best tuna salad is to have mostly tuna and be sparing on the other ingredients, using only what is needed for flavor. Especially be cautious on use of mayonnaise staring out adding it incrementally and stopping to taste test. Use only enough mayonnaise to reach correct consistency and maximum flavor then stop. It is tempting, but don't add a huge dollop all at once. Just little by little add more and more until desired point is reached. Stop there.