How do I balance intake of solids and liquids during an ironman?

You need enough liquids and electrolytes to prevent dehydration, having said this you should expect a 2-4% drop in weight by the finish line, so your aim is never to drink enough to maintain starting body weight.   You need fuel in the form of carbohydrates.  Whether this comes in the shape of solids, or liquids, or most likely a mixture of both is totally up to you.  Aim for a carb intake of 90g per hour, this is a lot more then a lot of athletes think they need.  So do your math and write out a plan with exactly what you are going to eat and drink, look at the ingredients and calculate how many carbs per hour your plan will give you.  Be specific for all stages starting in the warmup, not neglecting opportunities at the swim lineup and transitions.  You will be able to fuel more on the bike then the run, so make sure you use that leg of the race.  Bon appetite!