Lamp oil still
Lamp oil stills can be found in the Chemist's House in Rimmington and near Miltog's stall in Dorgesh-Kaan. Its one and only function is to produce Lamp oil. To do this, use Swamp tar on the Lamp Oil still, then use an empty oil lamp, oil lantern, or a Bullseye lantern on the oil still to fill it.
Lighting a bullseye lantern inside the chemists shop in Rimmington is one of the medium Falador Tasks.