Abstract: A retractable indicator assembly 10 may be mounted on a container C which transmits air through the container and removes deleterious gases with an activated charcoal medium M in the container. An elongate indicator housing 12 has a chamber 20 therein. A male adaptor 14 has external threads 16 for sealing engagement with the container. A plug 40 is provided at the upper end of the housing 12. Housing 12 includes a transparent wall portion 28 for viewing at least a portion of the chamber 20. A litmus indicator 42 is moveable by a retractable rod 54 from a retracted position within the container to an extended position within the chamber 20 of the housing 12. An outer housing 64 is secured to the upper end of the rod 54, and protects the indicator housing 12 while the litmus indicator 42 is in its normally retracted position.