Union couplers are used to join two pieces of pipe that you may wish to take apart at some time in the future. The pipe glues into either end and the two bits are screwed together, note these are not taps and the water must be drained before disconnecting to avoid a flood. PLEASE NOTE all our pipe is fully fish safe and has been used by us for many years, all joints are glue fittings using standard 'solvent weld' glue available from us or most DIY shops. All our pipework is metric and directly compatible with all European pipe such as VDL, it is also directly compatible with Aqua Medic Deltec Surchan and almost all European equipment. It will not fit directly onto most U.K. sourced pipework without a metric to imperial adaptor. If you are in any doubt please contact us for advice.