Lubricating glass joints

Depends what you're using the glassware for, if required an absolute minimum of petroleum jelly (I tend to use it as a temporary sealant, otherwise the joints need to be scrupulously clean and don't actually need lubricating.
 
I second purple cat.
I have a masters in chemistry and the grease was only for when you needed to put the apparatus under vacuum as the joints leak air otherwise.
The profs would take marks off if you used grease and it wound up in your product!
You clean joints to within an inch of their life (detergent, scrub, methanol, distilled/deionised water then acetone to dry) and keep them clean and they don't get stuck.
 
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