I have been spitting in the sink for over 3 years now. I have not had one clog. It's not that much oil, like you are pouring a bunch of grease down the sink. I do run the water after I spit it out. And I do regularly spray some antibacterial stuff into the drain.
Spitting in the toiliet is just gross. I can't believe what starts growing in there in a short amount of time.
The original Ayurvedic instructions is to pull while meditating on the toliet (or squatting somewhere), and then bury the spitum in mud.