I've been fighting a clogged bathroom sink for a few weeks. I've used boiling water, sulphuric acid, baking soda and vinegar, a shop vac (suck and blow), a water hose bladder, multiple types of drain snakes, and maybe some other ideas I'm forgetting to name. All of these options were added to the pipe via the stub in the wall under the sink. The best way to get to the clog is via the vent pipe in the attic. 

I can't use an automatic drain snake since the clog is in an offshoot of the main vent pipe. Meaning, it's accessible in the attic, but not accessable on the roof. From the stub, it won't snake down to the clog since it's a t-shaped pipe rather than connecting at a 90 degree angle from the stub to the clog. 

From the mark on the drain snake, it looks like the clog may be 14-16 inches vertically down from where the pipe drain goes from horizontal at the stub to vertical down the vent pipe. It's likely right above or directly level to the floor and about 8 feet from the ceiling. The wall stub is about 18 inches from the floor. From wall stub to vertical pipe, it's about 2 feet. It's a foundation home rather than pier and beam.

It doesn't seem like I can access the clog from the outside of the home where the toilet exits the home. 

The pipe is a cast iron pipe likely from the mid 1950s.

Videos:
1. https://youtube.com/shorts/c0B7fbjhSX4?si=Tfoi5dShpkSoYEmc
2. https://youtu.be/8vkwJm_RJKM?si=zSbjbClrU3gG8c5c
3. https://youtu.be/SoIgZFCMAnY?si=CuVaEetY6hk0_vDL
4. https://youtube.com/shorts/YMduHCqC31M?si=P9UwNtQa190FsIRc
5. https://youtube.com/shorts/zz-6jTQv-FM?si=zdbgSJTWl0cn-Kl7
6. https://youtu.be/RqZCWwnIIeM?si=UPMIXutY_XPYt0Cp


Any ideas feedback is appreciated.
What is it?
How do I unclog it?
How can I get the liquid out for a better image of the actual clog?

Clogged Bathroom Sink