Pipet made up of two transfer pipets, tandem-type, connected to a common reservior.One pipet fills while the other one empties. This filling/emptying cycle is controlled with the stopcock. Air bubbles are eliminated due to the gravity feed. Excess is returned to the reservior via side tubes. Teflon® stopcock has 2mm bore. The top standard taper (29/42) joint has a hole for venting. Supplied with stopper.