It depends on the size of the slings. I would recommend, for arboreal tarantulas, a 50 dram vial. They may be available at your local pharmacy, but you'd best just buy them in bulk online. For the terrestrial species such as many OWs and quite a few New-Worlds like the genus, Grammastola, I would mostly recommend a 32 oz. deli cup. You can get them at your local The Container Store (lol).