How to clarify questions to professors without seeming condescending?

I often ask questions to professors outside of class, on technical topics (I am a student in STEM) that I want to explore into, and I value their input. When I ask a question about something that is unusual in the technical sense, often the professors do not understand my question properly, leading them to not answer my question, but talk about something else (answering what they think is the question, but is not). Possibly this is due to the weirdness of the question, as in no student has asked this sort of question before, and I do have a tendency to ask unusual technical questions (often outside the syllabus of that course). In the middle of their answer, I know they are talking about something else, and I want to clarify the question again.

The question is: How do I interrupt them to clarify my question, without looking condescending and insulting? Or do I just wait till I finish their answer before clarifying it again?

PS: Although this is in the context of academics and student-professor relationships, this could potentially be extended to discussions between colleagues in the corporate setting, or any sort of mentor-mentee relationship as well.