Hi,
-
The most common reason for unexpected behaviour with obstacles is non-watertight or non-manifold geometry. Tip: you can highlight non-manifold geometry in object edit mode with Select > Select All by Trait > Non Manifold
-
Doubled geometry is also a common cause of leaks. For example, two identical triangles layered on top of eachother will cancel out and produce a hole.
-
If using the solidy modifier, this is something that you should be careful with. This modifier can produce non-manifold geometry in many cases, especially if the original mesh is complex.
-
Thin walled obstacles at a low resolution can also produce holes: Scene Troubleshooting: Thin obstacles, leaking fluid
-
We have a feature to contain fluid inside of an object that may be suitable for this type of simulation: Obstacle Inverse Workflow
-
The FLIP Fluids addon contains a debugging tool to help diagnose if your mesh is being recognized and resolved correctly within the simulation. See the first tip in this article/video for more info: 10 Tips to Improve Your FLIP Fluids Workflow in Blender.
Hope this helps! If you are still having trouble, attaching a .blend file could help, or you may send it directly to us through the Blender Market messaging system.