What is the best method of trying to find cracks in hoses?

spray it with soapy water and look for bubbles. If it's a radiator hose squeezing it can increase pressure in hose to reveal bubbles easier. You can also use a pressure tester on a cooling system (https://www.2carpros.com/articles/radiator-pressure-test), some auto parts stores rent or even loan this tool out to customers. Running an engine until it warms up will also increase cooling system pressure. If it's a vacuum hose, spray a tiny TINY amount of starting fluid in an area with engine running, if there is a vacuum leak engine will increase in RPMs momentarily.