Bladder tanks
My experience with bladder tanks was not good. We flew Cessna Agwagons/Agtrucks for years and when the bladders started leaking, they were over $1000 to replace, each! You also had to have gorilla-length arms to reach in through the HUGE inspection hole through which the bladders were inserted to snap the keepers in place to keep the bladders from collapsing from their own weight.......all this expensive, complicated and a real pain. Cessna claimed that they did this because of the ag aviation environment and that in a crash, the bladders would retain the fuel and help lessen the chance of a fire...baloney...my airplane burned to a crisp anyway when the pilot hit a roadsign and sheared off the right wing! Yes, he escaped from the inverted wreckage due to quick-release door hinges and only suffered a broken femur.
Pierre