Described herein is a transport tank trailer having a tank that can be used to more completely and effectively transport, store, load and unload a viscous product, such as a viscous liquid product, or liquid with solid(s) in suspension. Materials for transport, storing, loading and unloading include both food-grade and non-food grade products. Exemplary products include chocolate, paint, wastes, and asphalt. The tank system involves: a) agitation means (e.g., vibration devices) to force viscous product to flow during unloading; b) a heat-traced closed loop venting and unloading system resulting in the elimination of opening of the manhole on the tanker, which results in the release of heat; c) use of enhanced insulating materials to reduce product solidification during product discharge; and d) reduction of thermal bridges to increase product heat retention. The invention also involves an inventive cargo tank shape that promotes viscous product discharge during unloading of the tank. The viscous product trailer can further comprise a heated make-up air system operably associated with the tank housing. The system can provide heat vented air and heated air into the tank interior containing viscous product so as to maintain tank, and consequently product, temperature.