I had an Avistar that I flown more than 50 flights with a 40 FX and absolutely loved it. I recently sold it to a buddy as it's such a great trainer. The fuel tank issue sounds all fine, I only used two lines and ran the supply line up and back down to the nipple on the engine for ease of refueling. Using the third for servicing is probably even better. Install the tank with the neck through the hole and tank against the supports in the fuselage and everything will work fine. Have fun with it!