Sounds like you've had great results! But I just wanted to chime in to say: it's not the tides. That's just not how they work. The lunar tidal force is only strong enough to impact the depth of even large bodies of water hundreds of miles across like the Great Lakes by no more than 2 inches. The tidal force on your balls (which, while big, aren't quite
Great Lakes-sized yet) is infinitesimally small, especially compared to the vacuum forces you're pumping with. A hair in the tube is going to put more force on you than the lunar tide will.
Not saying this to be an annoying science pedant. I just don't want you wasting time sitting around waiting for a particular time of day when you could be in the tube getting huge.