Abstract: A portable holding and mixing tank system for at least two dissimilar liquids includes a tank having at least two fluid-isolated holding compartments (e.g., separate tank units or a dividing wall within the tank interior space) for holding a respective one of the dissimilar liquids. A manifold assembly defines respective channels for the dissimilar liquids and for pressurizing fluid supplied from a source thereof. The liquid and pressurizing fluid channels are fluid-connected to each of the holding compartments. A pressurizing supply conduit fluid-connects the source of pressurizing fluid to pressurizing fluid channel, while liquid supply risers respectively fluid connect the dissimilar liquids contained in each of the holding compartments to the liquid channel defined by the manifold assembly. A liquid discharge port fluid-connects the liquid channel defined by the manifold assembly.