I have the same problem sadly. Although before you start shitting on me for being stupid I MEASURED the marbles to make sure they would fit in my 19mm joint. They were but I didnt realize inside the joint it gets a little smaller. As a result I now have a fucking marble stuck in my downstem joint.... woo. So instead of weighing my piece down for some dope new ash catchers (that are too heavy without some extra weight) I have a waterpipe with a marble.... ANY IDEAS are helpful. Also again, Fuck you if you are going to shit on me for being "stupid" and measuring the marble before I weighed my piece down.
People aren't shitting on the getting the marble stuck thing....They are shitting on how incredibly stupid even considering putting marbles in your bong is!
A bong is like an asshole, and this forum is like a proctologist office, full of people who are sticking things where they do not belong!