Are there any halachot that apply the rules of kashrut to the cup I use to wash my hands before I eat?
This answer says that one can use "any cup". This site says that a cup can be drunk from and the water can still be used so I thought that this meant that the cup for washing doesn't have to be a dedicated washing cup and can be used for foodstuffs otherwise.
If I am about to eat a cheese sandwich, may I wash with a handled cup that was recently holding beef gravy but has been rinsed out? What if the cup held a non-kosher beef gravy? What if the cup held nothing, but was washed in hot water with dishes that were used for milchigs/fleishigs/treif food -- is there a "status" to the cup that could contraindicate its use at particular times?