I agree that the pitots on the Firebird do experience negative pressure at times during a flight. The thing that does not make sense to me, is that unless the pitots were plumbed with clunks into the tanks, why would they both produce a solid enough flow to cause the very visible trails? Would not the fuel all be at the back of the tanks in a pull to vertical? Also, it appears that this vapor trail can happen at any time during the flight, which means it is not effected by fuel load.
We've all found fuel residue around our fuel vents. But only the Firebird has a visible trail. There are still too many questions to be answered, for me to be convinced. If I could just win the Lotto, I would buy one and find out.