@JamesWorldSpace Maybe worth trying: insert a 1m diameter nylon tube (or shorter set of tubes for most difficult sections) through cave network & inflate with air like a bouncy castle. Should create an air tunnel underwater against cave roof & auto-conform to odd shapes like the 70cm hole.
@StrainCentral I dont feel this is a yes or no question. I can smoke like a champ and still function and problem solve. But I have homies that make me@nervous when they get high