During the process of inspecting each rivet for blue fuel dye stains, my heart sank when I found a rivet hole without a rivet.
In the photo above, I have an alignment punch stabbed through the proseal filled hole. After much thought, and consultation from VAF, I decided to countersink the hole to accept a countersunk closed end blind rivet. The pictures below show before and after countersinking. For good measure, I was able to contort a piece of AL to slather a blob of sealant on the shop head of the rivet. The good news is that even if it didn't seal completely, the location of the rivet makes it highly unlikely to leak.
I leak tested my first tank about a week after completion (November) using the schrader valve and balloon method. After a few attempts at getting the balloon to seal on the vent line, I sprayed soapy water liberally over every rivet. Success!! Leak Free!! Fuel Tank Complete!! Not so fast.....
My second tank was completed not long after the first but for whatever reason had not been leak tested. I got busy with wings and basically kept putting it off. One day I came across a thread on VAF regarding the difference in flaring tools, automotive vs aircraft. I decided to read a little deeper since I bought my flaring tool (used to fab the vent lines) from autozone. I then went down a whole different rabbit hole on what happens if the mismatched tubing flare and AN fitting are mated since one is 45 degrees and the other is 37 degrees. A potential leak path between the internal tank bulk head fitting and fuel vent line could be a problem, causing a constantly dripping fuel vent to venting and fuel feed issues. I decided I needed to halt all work on the wings and circle back to my tanks and see if I had a leak. I used about 6-7 gallons of 100LL to test the tank. I placed the tank in its cradle and laid it down, filled with gas, for a few days. There was no evidence of leaking any where.
I didn't get any photos of what I'm about to describe but next, I propped up the outboard end of the tank so that the entire inboard baffle including the vent fitting would be covered in fuel. Once again no leaks leaks were found, but that doesn't mean that I'm free and clear. Once the plane is flying, vibrations or what not could case the fitting to begin leaking at which point I'll have to decide what to do. The proper fix is to replace the vent line with a properly flared fitting. However, the only access to the inside of the tank without cutting a hole is through the fuel float hole.