"Ganga was born from Shiva first and then Shiva gave it to Brahma. Brahma sprayed some portion of Ganga on Vamana's feet and some portion of that Ganga came to Jata of Shiva. Gautami Mahatmya of Brahma Purana mentions it." @The Destroyer
Innumerable Srivaishnavites cite the Ganga's advent from Vishnu's foot/feet to "jata shankari" (as Tulsi das put it) as evidence of "Vishnu Paratvam". But not one scripture cites the whole journey. We have Siva receiving the Ganga and also Vamana's feet being sprayed or his foot piercing the dome of the universe to release the Ganga but these are unconnected events in the puranas. They have been connected only after they have been written up separately. If I stepped into a river and at some unspecified later time the river wet someone's hair - it is is not necessarily true that he is receiving my "footwash" as they say in Indian English.
Not the answer you're looking for? Browse other questions tagged shivaganga .
Like any library, Hinduism Stack Exchange shares great information, but does not offer personalized advice, and does not take the place of seeking such advice from any Acharya, Pundit, astrologer, Guru or other trustworthy Counselor.