I don't think that you will have a problem.

If it was too stiff with the method Minn posted, then it's probable that the stiff portion was too long. You only need a short portion of the stiff stuff to avoid the kinks and maintain the effect.

Don't worry about using the black stuff (even if it's for gas).
My understanding is that the black stuff is good for everything Gas / Smoke / Glow) but the regular silicon will get eaten by the gas / smoke fuels. (someone PLEASE correct me if that is not accurate).

I don't think you have done anything wrong. I've never run two clunks so that may just be an innovative solution. However, to me it seems like overkill and could cause some issues in the future (like twisting). Perhaps Minn knows a pro vs con against multiple clunks. Not my area of expertise. Anyway, the key is that you don't have a problem with the kinks. I would still try to find the "happy place" with the small portion of stiff tubing in the tank that allows freedom without the kinks.

It will help out in future models for sure. I don't think that dual clunks will be practical from here until the day that you stop flying.