I got 3 new tanks but they don't really stay together. The carto just slides and the liquid leaks out. Any ideas?
Looks like this one:
https://www.fasttech.com/products/0/10007238/1600900-splash-anodized-glass-carto-tank-kit-6-0ml
Some folks have complained that the tanks slide off too easily on these, others don't seem to have had a problem.
Might be a manufacturing-quality issue?
Tighter-fitting o-rings would probably solve the issue, but making the fit TOO tight will make the cartos hard to insert/remove. I'm not sure the exact size that is in those tanks, but try one that is just slightly thicker. For example, if the o-rings in it now are 2mm thick, try 2.5mm ones, etc
There are worthwhile things on Fasttech, and, there are not so good things.
Did you read the comments and reviews?