I've come across two spellings for this word. Siphon and syphon are apparently both correct. English is not my first language and this word is not used often in practice, especially in written form. I am very curious about this. Is there any reason to prefer one over the other? And which spelling would be more common? Is it a regional thing (like maybe American like one and British the other) or something else. I wonder if this is a specific case of more common interchange between i and y in some words - which would be interesting.
Wikipedia suggests that siphon may be more common spelling.