Accu-sink problems. I am in need of suggestions for inner tube replacements. I believe the original tubes were R-13" auto tires, but am only guessing. I have been unable to find this size. My 20+ year old system has most of the original tubes, however one has recently failed. I have substituted R-15 and small lawn tractor tubes but within a couple air cycles they have all popped in various places. I suspect the issue is that this size is to large/small for the submarine and folds over on itself during inflation and creates excess pressure. Boom! I have carefully inspected the inside of the sub as well as the sand too. I filled the cavity on the cap interior. I contacted Wally at Wally sinker but no ideas/suggestions. Now I turn to the Forum.