If you have ever hired an exterminator and watched them perform your service, you will generally find two things...one, they are NOT rocket-scientists, and second, MOST do not want you to watch how simple it is to solve your problem. If you have those "big,black ants", most likely you have a Carpenter Ant condition, in which finding the nest isn't as important as most think. Micro-encapsulated Diazinon, such as KnoxOut 2FM, and a $85.00 Solo BackPack sprayer used diligently will do a much better job than the exterminator who wants to charge you big $$$ will make you think. Spray 4' up the side of your house, out 12'-15' from your house (those are feet, not inches), and a 6' band along your entire property line perimeter. You should end up using about a gallon of mix for every 200 sq. ft of house, and another 5-8 gallons of mix to get your property lines done well. Hit the bark-dust with ruthless abandon, and ease up on the grassy areas!!!! Get all firewood away from your house. Get under your house to see if there is sawdust being kicked out of the cracks of your flooring. If so, use a product called "Bora-Care" and a good 1-gallon pump sprayer to spray the underside of your floor Bora-Care will PENETRATE 4"-6" right into wood and make your 2X4 T&G flooring poisonous to ants, termites, white, and brown fungus. It's about $100.00 a gallon, but very much worth it!!! In short, if you plan to live in the house for awhile and don't be intimidated by environmentalists thatl tell you about the immediate toxi-ability of general use insecticides, you can do a professional quality job with such a treatment 2-3 times each year. Don't need to "drill your walls" if you will keep up with exterior sprays...you cannot have a nest any bigger than 3K-5K ants in your home unless you have huge amounts of rotting timber in it. Look for stumps, sick trees, firewood piles, and railroad ties for your little beasties. I've been an exterminator for over 4 years, self-employed, done over 600 Carpenter Ant jobs, and never used anything more than good "juice", a backpack sprayer, and a hand-held sprayer. You can do it.
p.s., don't use the diesel!!!! You'll be sorry!!!!