Auxiliary fuel tanks are provided with an inner barrier wall defining an interior volume for containing aircraft fuel, an outer barrier wall adjacent the inner barrier wall so as to define a space therebetween, and a drain part having a port in fluid communication with the space to allow leaked fuel within the space to be discharged therefrom. The drain part may be positioned at a corner junction between at least side and bottom walls of the outer barrier wall. In some advantageous embodiments, the drain part is positioned at a corner junction between the side wall, the bottom wall and an end wall of the outer barrier wall. One or more drain parts may be provided on each auxiliary aircraft fuel tank. If a plurality of drain parts are provided, then each drain part will preferably have a port in fluid communication with the space between the inner and outer barrier walls to allow leaked fuel within the space to be discharged therefrom, and each drain part will be positioned at respective corner junctions between at least side and bottom walls of the outer barrier wall, preferably between the side wall, the bottom wall and an end wall of the outer barrier wall. Aircraft may thus be provided with one or more of such auxiliary fuel tanks.