A Klein bottle only makes sense if it’s transparent so you can see what’s going on inside. Not that easy to make transparent/translucent 3D prints. Here you can see 3 different Klein bottle prints using an Anet A6 3D printer and Rigid.Ink Trans Blue PLA filament.
The leftmost bottle is a 0.8mm solid double-wall print – even back-illuminated you cannot see what is going on inside.
For the middle Klein bottle – I have cheated. That is a 0.8mm solid double-wall print of a half Klein bottle – the bottle has effectively been cut right through the middle, at least that way it is clear what is going on inside.
The right-hand Klein bottle is a 0.8mm SINGLE-WALLED print! Being translucent you can at least see what is going on inside.
I think we need a 3D glass printer to get what I’m really after.