Passive dosing is increasingly used to control exposure concentrations of hydrophobic organic chemicals (HOCs) in small sized aquatic tests. However, there are increasing demands to conduct ecotoxicological and bioconcentration/bioaccumulation tests in complex matrices for long exposure periods and in large scales. One challenge for upscaling passive dosing is that the mass transfer from the passive dosing donor to the exposure medium is diffusion limited. Another challenge is that the longer test duration often required for larger sized organisms can lead to the formation of biofilm that can limit mass transfer or even degrade the test substance. In order to fill this gap, this study introduces in tube passive dosing (in tube-PD) as an approach to control HOC exposure in larger test volumes and flow-through experiments: Aqueous medium is dosed by pushing it through a tube holding HOC loaded silicone rods. We equipped a 6 meter PTFE tube (ID 10mm) with four parallel silicone rods (OD 3mm) to accommodate water flows from 0.2-120 L/h, and developed a mass transfer kinetic model to capture the chemo-dynamics in the system. The first experiment was conducted with fluoranthene, where aqueous concentrations were measured by molecular fluorescence at different flow rates, water volumes and positions within the tube. The second experiment was conducted with a complex petroleum mixture (cracked gas oil, UVCB), where concentrations of 22 mixture constituents were measured by solid phase microextraction coupled to GC-MS. Overall, the system provided stable and reproducible water concentrations, which were at equilibrium for flows <10 mL/min and at steady state for higher flows. Fluoranthene concentrations declined <20% when dosing one m3 during one week. The mass transfer kinetic model provides mechanistic insight of the partitioning kinetics and can now be used to scale the system for various applications.