You should probably ask about Simulation in the Simulation forum.
To get the correct weight for your simulation, you will probably need to model the liquid as well. In your assembly, add a new part that will be the liquid. Make it larger than the volume that the liquid will fill. Use the Cavity feature to subtract the solid part or parts from the liquid.
thank you sir
Yes this should be moved to the Simulation forum.
The liquid modeling depends on your interest - if you just need the weight transferred to some other component do as Jerry suggested, but if you want stresses on the liquid container I would not model the liquid or apply it as a normal force, but rather use a pressure load which varies with height, starting at zero from a defined CSYS at your fluid top (for open systems) or adjust to some other reference interal pressure. This will properly apply hydrostatic loading based on what you put in for the coefficients as calculated from your fluid specific weight.
For the mesh, begin with default Curvature-based (on draft if it's complex), then add refinements as your stresses dictate. Sim for the assembly is no different than a part.