A stormwater treatment device for removing floatables, solids and suspended particles and the like from stormwater run off, whereby a removable assembly is provided for installation into a manhole basin, the assembly including a pass-through member which receives stormwater from an incoming drainage system, and diverts low flows to at least one or more vortex separators, while allowing for high flows to bypass the separators and flow through the assembly untreated to exit the basin without diversion.