That was my problem, they worked fine at first, but then would start leaking, I'd mess with it and it would stop leaking for a week or two then start again. I finally just gave up after trying several different styles.Then they started leaking. Too lose, too tight, like an old toilet, the O-rings could only do so much. Spent the $$$ to buy a bunch of PVC tees off of Amazon, pre threaded 1/8" NPT. Haven't had problems since.
I have seen the PVC Tees on Amazon and was wondering if they would fix the issue. I think I will go ahead and take the plunge and get some now. I like to have different options for the youngsters to have clean water.