If someone has a juice canister that does not allow the ice to come through. Can one use it on shabbos as long as the last person to use it allows some juice to remain in the canister with the ice when the canister eventually gets low on fluid? Can multiple people use it?
Yes, the canister may be used. However, when the juice is finished, it should not be used to take out the last drops of juice, and retain th ice.
The reason for this is that general pouring from the canister is not considered an act of separation, but an act of pouring. Only the final drops might be considered an act of separation. This is based on the ruling of the Mishnah Berurah concerning pouring out liquid from a container, and leaving the sediment behind.
[Even for the final drops, a number of poskim, including Maharit, maintain that there is no taaroves (mixture) between liquid and solid; however, the Mishnah Berurah mentions the stringecy of the Taz with regard to a fly in one’s cup, which assumes that solid/liquid is considered a mixture.]