Abstract: In a liquid handling station taking up and dispensing liquid through one or a plurality of pipettes each having a syringe and a respective nozzle, it is customary to fit the nozzle(s) with a disposable pippette tip(s) which is replaced between samples to avoid cross-contamination. There are difficulties in reliably fitting and sealing these pipette tips onto the nozzles. The present invention simplifies the fitting and sealing of pipette tips onto nozzles by forming each nozzle with an annular groove having a controllably variable axial width. An elastomeric O-ring seal is fitted in each annular groove. The nozzle and its fitted O-ring seal is inserted into a pipette tip, and then the axial width of the annular groove is controllably reduced to cause a circumferential expansion of the O-ring seal. The nozzle and the pipette tip become mechanically and sealingly attached without the pipette tip having to be force-fitted onto the nozzle as was previously necessary.