Absorbent plugs and caps plug or cap fittings that have been used to inject liquids into various systems. The plugs are sized to fit within the interior body cavity of fittings to absorb the residual liquid that is left in the cavity after use. The caps are sized to fit over the exterior of the fittings to absorb any residual liquid that leaks out from fitting exterior surfaces. The caps can also have interior plug extensions that extend into the interior cavities to also absorb the residual liquid from the interior. The plugs have non absorptive tabs for insertion and removal and the caps have non absorptive exterior skins or coverings to contain the absorbed liquid within the cap. One such use is to plug and/or cap fittings such as R134a service couplers which are used to inject dye into automotive air conditioning systems.