Locate a place as close to the thru-hull vent as possible. Mounting the filter on the backside of cabinets, walls or other interior bulkheads are a good place. Having easy access is always a plus for future filter service. Locating the filter at the tank is OK but overfilling your waste tank can allow waste to plug the intake side of filter and would require removal of filter to clean / clear the blockage of filter passage before filter would work properly. Note: "Blocked vent line can cause damage to your holding tank"