Plays a role in vesicle-mediated protein trafficking to lysosomal compartments including the endocytic membrane transport pathways (PubMed:26783301). Believed to act as a core component of the putative HOPS and CORVET endosomal tethering complexes which are proposed to be involved in the rab-5-to-rab-7 endosome conversion probably implicating sand-1, and via binding SNAREs and SNARE complexes to mediate tethering and docking events during SNARE-mediated membrane fusion (By similarity). The HOPS complex is proposed to be recruited to rab-7 on the late endosomal membrane and to regulate late endocytic, phagocytic and autophagic traffic towards lysosomes (By similarity). Within the HOPS complex, contributes to the normal development of gut granules in the adult intestine (PubMed:15843430, PubMed:24501423, PubMed:25273556). The CORVET complex is proposed to function as a rab-5 effector to mediate early endosome fusion probably in specific endosome subpopulations (By similarity). Required for recruitment of vps-33.1 to the HOPS complex (By similarity). Required for fusion of endosomes and autophagosomes with lysosomes; the function is dependent on its association with vps-33.1 but not vps-33.2 (By similarity). Probable core component of at least two putative endosomal tethering complexes, the homotypic fusion and vacuole protein sorting (HOPS) complex and the class C core vacuole/endosome tethering (CORVET) complex. Their common core is composed of the class C Vps proteins vps-11, vps-16 and vps-18, which in HOPS further associates with vps-33.1, vps-39 and vps-41 and in CORVET with vps-8 and vps-33.2. Cytoplasmic, peripheral membrane protein associated with late endosomes/lysosomes. Viable with a reduced number of gut granules in the adult intestine (PubMed:15843430, PubMed:24501423). Embryos of these adults arrest in early development and lack gut granules (PubMed:15843430). Endosome/lysosome fusion defects in coelomocytes (PubMed:26783301). RNAi-mediated knockdown results in a reduced number of gut granules in embryonic intestinal cells (PubMed:24501423). RNAi-mediated knockdown results in defective endosome maturation with the accumulation of small vesicles near the gut lumen and large endosomes/lysosomes on the basal side of the cell (PubMed:25273556). Belongs to the VPS16 family.