缶 used to be a pictograph of an earthenware vessel or container with a lid on top. At some point it seems to have been adopted as abbreviation for 罐. Since the Chinese Text Project’s dictionary lists both fǒu and guàn as words for 缶, that usage may have it’s origin in Chinese. In Japanese the Sino-Japanese for 缶 is only kan (like 罐). In 罐, 雚 acts as phonetic.
The modern Japanese meaning of 缶 kan came into existence when 缶 (or 罐) was loaned to stand for the Dutch word kan (especially insofar Dutch kan stood for a cylindrical metallic container). English can is related to Dutch kan, and seems to have influenced the later usage of 缶 in Japanese.
Henshall (1095) discusses 罐. He writes that heron 雚 is ‘acting phonetically to express pour and possibly also lending loose connotations of accommodate/ take in (from a heron’s ability to consume large quantities of fish)’. Leading to ‘vessel for pouring liquid into’.
The phrase ‘X is acting phonetically to express Y’ is one that Henshall uses a lot. Often it’s unclear where Y comes from or why Y would come to mind. In this instance 灌 must be the intended word (Schuessler has guàn 灌 with ‘to pour out; libation’ as the first meaning).
罐 sounds the same as 灌, uses the same phonetic as 灌, looks semantically related (to pour a liquid - that in which one pours a liquid) and is clearly listed in both dictionaries for ancient and modern Chinese. ¹
It may even be possible that 雚 is the protoform of 灌.² But even if 灌 was not at some stage written with 雚, then the phonetic it shares with 罐 seems more than just convenient. Thus far it seems to me that Henshall’s way (following scholars like Katō Jōken no doubt) of interpreting the phonetic (not just sound, also a meaningful word that the sound points to) is most convincing when the two words are actually related.