A magnetic rod guide for a filter is provided that includes a base for attachment to part of a filter, a through aperture through which a magnetic rod can move, and resilient engagement device. The resilient engagement device includes one or more resilient latches for holding the magnetic rod in one or more fixed positions relative to the guide. Each resilient latch is adapted to allow movement of the magnetic rod through the through aperture in either direction, for insertion into the flier or withdrawal from the filter into one of the fixed positions.