remember this....a fuel tank is never empty. It's either full of fuel or full of air or a mixutre of the two. When you put fuel in, air must be vented out. If fuel is blowing back out the fill line then the vent (going to the muffler is clogged). Or you are filling from the vent line. Fuel coming out the muffler means a full tank.
When filling the tank disconnect both lines and fill until fuel squirts out the vent. fill from the line that goes to the needle valve. You cannot fill from the line that goes to the muffler, or you get the result you described.
When the tank is installed make sure you have no kinked fuel lines,
Yes a loose fuel tank will cause dead sticks. I have an Ultimate Bipe after coming out of a series of snap rolls the engine died, brought her in and everything seemed ok on the ground. next flight she dead stick again at some point.. took her home and found the stick that held in the aft tank plate had come loose letting the fuel tank slide around..glued in a beefer stick on more problems