Apparently the female seminal receptacle is also very long. In fact, the increasing length of this receptacle is one of the explanations for the extreme sperm length.
Drosophila females have evolved to fertilize their eggs with particularly long sperm. Only large, healthy males are able to produce large quantities of gigantic sperm, and if a female reproduces with healthy males, her offspring will have genes that make them healthy, too.
https://blogs.iu.edu/sciu/2023/05/06/the-longest-sperm-on-earth/
Apparently the female seminal receptacle is also very long. In fact, the increasing length of this receptacle is one of the explanations for the extreme sperm length.