Thread a thin string down the tube. Tie a cotton ball or small rag on the end that is just barely big enough to be pulled up the tube. Slide the tube into the oil to be samples. Wait a second for the swab to get soaked with oil, and then pull it out quickly. Be sure the outside end of the tube is lower, like at ground lever, than the engine end.

I think that you are pissing in to the wind though. Syphoning oil thought a tube small enough to go down a dipstick hole is a slow process on a good day. I would suggest cleaning the area around the pan drain plug very well. Use starting fluid or the like. Loosen the plug, put a clean container under it, then remove it just slightly for your sample.

When I worked in the marine industry in the Middle East we used top sample all the engines frequently. We used Mobil Oil samplers that came with their own little disposal plastic suction pumps. They looked like small concertinas about 2" in dia.

The thing to be watchfull or is that you don't contaminate the sample.