I want to suck the sour crop liquid out with a feeding tube from my chicken's crop but

[Eggcessive]

I really can’t answer that. If it were that simple, sour crop would not be so difficult to treat. @casportpony have you tried aspirating material from a sour crop, or flushing one and has it worked?

 

[casportpony]

I have tried aspirating it, but was not successful. I think it's because the opening of the tube is too small.

 

[Shadrach]

I was just wondering if anyone has done this and knows how far down the tube should be inserted. I watched a video, and she put the tubing in but she could not pull the syringe out which I felt she was hitting something solid or was it because she didn't push air in first...idk.

If the situation is critical and the assumption that it's straight forward sour crop is wrong, or even if it isn't, might not crop surgery, which has been successfully done and there are videos and advice on how to do it available, be a better option. You would have the benefit of being able to see the crop contents as well as being able to clean it out properly.
You may not be up for it and I wouldn't blame you; I've never done it and I'm not sure I could, so bear this in mind when and if you consider the option.

 

[Debbie292d]

If the situation is critical and the assumption that it's straight forward sour crop is wrong, or even if it isn't, might not crop surgery, which has been successfully done and there are videos and advice on how to do it available, be a better option. You would have the benefit of being able to see the crop contents as well as being able to clean it out properly.
You may not be up for it and I wouldn't blame you; I've never done it and I'm not sure I could, so bear this in mind when and if you consider the option.

@azygous has. https://www.backyardchickens.com/threads/emergency-crop-surgery-question.1607576/post-27944019

Another comprehensive explanation a member shared they had followed that worked for them: https://www.greenwillowhomestead.com/blog/how-to-operate-on-your-chickens-impacted-crop

 

[casportpony]

Is this the video you watched?