nothing works properly with non-manifold geometry, max just doesn't let you create it cleanup will find usually find your problems - it won't necessarily fix them properly - usually telling cleanup to select and then manually deleting the problem components will get you there. Alternatively, one thing that can help is…
I see this sort of complaint fairly often. While Maya is unforgiving, and frankly a fucking awful modeling tool it is entirely possible to manipulate geometry without generating shite - I do it all the time, as do many others. If you find yourself having to clean up your own work all the time you need to reassess the way…