Emergency drainage is an important passive safety function in liquid-fueled advanced reactors. A physically consistent post-drain assessment requires a common definition of the material transferred to the drain tank for both neutronic and decay-heat calculations. This study develops a region resolved, conservation based depletion to drain framework for the emergency drain tank (EDT) of a Dual Fluid Reactor (DFR). The source generation scenario represents 365 full-power days of irradiation at 3.00247 GWth, without online fuel feed or fission-product removal. The main core, lower distributor, and upper distributor fuel inventories were transferred to the EDT, while the separately depleted breeder was excluded according to the physical drainage boundary. The resulting post-drain inventory contains 1363 nonzero nuclides, 1.5242×10²⁹ atoms, 21.69 t of isotopic material, and 6.159386 m³ of fuel. Decay-only evolution was evaluated using depletion chains based on ENDF/B-VIII.1 and ENDF/B-VII.1 and independently verified using a separate CRAM48 decay matrix calculation. For the ENDF/B-VIII.1 reference trajectory, decay heat decreases from 168.033 MW at shutdown to 15.859 MW after 1 day and 0.6436 MW after 365 days. Including the non-draining breeder would overassign the EDT heat source by 3.89% at shutdown, 11.05% after 1 day and 0.60% after 365 days. At 1 day, this transfer boundary effect is nearly three orders of magnitude larger than the 0.01396% difference between the two evaluated decay chain calculations. The deterministic pointwise upper heat history releases 61.86 TJ during the first year. The framework provides a verified source basis for subsequent post-drain criticality and heat removal analysis.