The presence of seroma after breast tissue expander (TE) insertion for a long duration can cause infection and purulency; thus, obvious fluid collection around TEs should be drained as early as possible. However, due to the risk of puncture, it may not be possible to completely drain the fluid if it is located above the TE. To manage such cases, we used an 18-gauge blunt cannula and achieved good results. Among 98 cases in which breast reconstruction was performed with a TE, 5 patients had symptoms of infection with fluid collection just above the TE. In all 5 cases, resolution of the infection was observed in an outpatient setting without the removal or puncture of the inserted TE, by performing a drainage technique using an 18-gauge blunt cannula. An 18-gauge blunt cannula minimized the risk of expander rupture during drainage and enabled the complete aspiration of fluid, even when it was located just above the TE; thus, the resolution of infection with the preservation of the expander was possible in cases that would otherwise have been impossible to treat without the removal of the TE. This drainage procedure using an 18-gauge blunt cannula is considered to be simple, safe, and sure, with benefits that exceed the risk; thus, there should be no reason to hesitate in performing this drainage procedure, even in cases involving slight fluid collection around the TE.