The main source feeding the abyssal circulation of the N. Pacific consists of dense, waters that pass northward through the Samoan Passage and are strongly mixed therein. A significant secondary source consists of water that approaches the Samoan Passage from the south but is diverted around the east side of the Manihiki Plateau. In order to gain insight into the factors that control the partitioning between these two flows, we develop an abyssal and equator-proximal formulation of the Island Rule. Evaluation of the corresponding circulation integral leads to the identification of dissipation and frictional drag effects within the Samoan Passage as a crucial element. The corresponding terms are estimated using observations recently collected by M. Alford and G. Voet (SIO) and colleagues. Estimates of the transport east of the Manihiki Plateau based on this approach moderately underestimate the observed transport, but the conclusions regarding the role of the Samaon Passage remain robust. We explore implications for the role of each branch for N. Pacific abyssal mixing and upwelling.