If that nozzle is going to have any serious loading on it, I can almost guarantee that you are going to need some teflon joints to protect those nozzles. I wouldn't bother with trying to calculate a flexibility on them as their load capcity is going to be so low already that it probably won't be worthwhile. Especially if you are hooking any kind of metal pipe to those nozzles. If the pipe is FRP also, anchor as close as possible and push the expansion away from the tank.