What is the procedure for checking the fuel bladders for leaks? How long should the fuel bladders last?

From what I've read on this forum you can expect a new (not reconditioned) fuel cell to last between 20 and 40 years. Apparently, keeping them full and the aircraft out of the sun are important for fuel bladder longevity.

I think the way to really test them is to take them out and blow them up with air. But supposedly, if you fill the tanks all the way up and wait a few days you may notice a drop in the fuel level, a fuel smell, and blue staining on the wing skins.

This info may be inaccurate, since I don't even own a Comanche (yet). I'm simply regurgitating what I think I've read.

While in the wing the only way I'm aware of is to fill them to the very top and wait a few days. A telltale smell in the cabin means a very slight leak, usually from cracking at the top. Blue stains indicate a more significant leak. A drop in fuel level is indicative of a serious leak that needs to be addressed soon. A new set of bladders properly maintained should last over 30 years. As previously mentioned, keeping them full so the tops don't dry out and hangared out of the sun helps a lot

I usually find main tank leaks by removing the wing root fairing and feeling whether it is sticky at the base of the butt rib from the point that the fuel line comes out, back to the main spar. The aux tanks usually show me stains under the wing, either at the access panel forward and outboard of the landing gear or along the main or rear spar.

Thanks Comanche flyers. MERRY CHRISTMAS