I can pick up my bong, I can smoke it, I can show it to other people, they can smoke it.
In the absolute broadest sense, you can use science to confirm it exists, by proposing a hyposthesis;
"My bong exists"
This is not a hypothesis, it's an assertion of fact. To form a hypothesis, you need a collection of facts. The hypothesis is the framework in which you connect those facts. A good hypothesis will not only explain the facts but also account for any disparity between them.
Then you can perform an experiment and smoke from it, this verifies your results. After verifying it for yourself, it's time to replicate the experiment; so give the bong to your friend and let him/her smoke it. If they can see it, grasp it, and smoke from it; you have replicated your results and have successfully verified that the bong exists.
You have only established a fact. Facts are observable and verifiable. Anyone can look at them an make the same identical observations or measurements. "My bong exists" is just a fact that people can verify.
For 'things that exist' an experiment like this is very doable. Depending on what objects are used, you may need to use different equipment to measure with. You can't very well grasp X-rays, but we certainly do have things to measure X-rays with, that's to say X-rays have a definite measurable interaction with reality.
An experiment is meant to test some sort of prediction. Because your assertion that your bong exists is simply a fact, no predictions can be made from it. Handing your bong to a friend so that they can verify it is not a test.
Measurements are careful observations. From careful observations we establish facts. Once we get enough facts, we start building a framework to hold them. This framework is called a hypothesis. Any hypothesis can sit there and hold the facts, but to become a theory it must hold the weight of those facts on two legs. It must be able to explain, and it must make accurate predictions. If your hypothesis does not account for all facts, then your ability to explain is weakened and your "explanatory leg" may not support the weight. If your hypothesis connects the facts in such a way as to be unfalsifiable, then you prevent it from ever constructing the second leg, predictability. If you can, through logic, see the implications of the way you connected the facts, then you can make predictions about additional facts we can find; you are testing the hypothesis. If you go looking and do indeed find the facts you expected, then your hypothesis has made an accurate prediction. It has passed a test and now grown both the legs it needs to become a theory. Of course, as the weight of new facts get added to the framework, these legs will continuously be strained and if you are unable to modify them, the theory will topple.
Remember, these legs can only be built from the framework, and the framework is built from facts. When to be suspicious is when a theory tries to replace one or both of these legs with something else, such as conspiracy. A conspiracy may look like support, but it actually renders the theory unfalsifiable, so it prevents any cogent predictions. For example: if a second gunman was involved in the JFK conspiracy we can predict that we will find evidence, facts, to indicate this when we go looking. When we allow conspiracy to masquerade as evidence, we make it impossible to verify this prediction because we have no way of knowing if the facts just aren't there, or if they have been removed by the conspiracy. There is no test we can do, and so there is no way to build our second leg. In this case conspiracy theorists go looking for something else besides facts, they look for anomalies. Anomalies present an apparent disparity between facts, in other words they create a gap, and then the theorists attempts to fill this gap with conspiracy. But notice that this only strengthens the explanatory leg and does nothing to give us the second leg. We have no power to predict and so we are left with wildly differing and often conflicting conspiracy narratives each unable to demonstrate they say anything accurate about the world. There are many other things people try to weave into the framework to count as facts: emotion, consequences, appeals to bad logic; but none of these allow us to build the support a true theory requires, and so these ideas crumble from the slightest pressure, like a house of cards.