I use mostly Sullivan and sometimes Dubro but I have never had a leaking fuel tank in 8 years. Its not talent here either, Maybe your not assembling them right?

There are many rules with Arfs, One of my main rules is to throw out most of the hardware that comes with an Arf and I never ever even remotely think about using the fuel tank that comes with it. If you are, thats your problem.

Now many will disagree and thats fine, you want to stop the problem, chuck the tanks.