i think it is better be safe than sorry
getting tested wouldnt hurt
You have a potential however low of exposure More likely to hepatitis A you also need to consider your hobbies.
Was someone else using the plastic tube before you used it? If so if they were just using it for smoking? If they just got saliva on it your risk is very low or no risk really if you are worried about HIV. Really, I don't see much risk if it was just used for smoking and you know who used it. If you don't know who used it and you think someone could have used it for sex that is different. As for licking your stool when you were a kid it was a long time ago don't worry about it. If you do it now don't do it. It carries some risk if you happen to have a bad type of bacteria or parasite in your gut and ate it now you could get sick or reinfect yourself. But I wouldn't worry about a past infection.