Reverse pressure tap
This is a rather old form of tap but it is quite possible to change its washer if needs be using readily available replacements.
A valve inside the tap enables the washer may be replaced without the need to switch off the water supply.
Wrap a cloth around the hexagonal nut above the nozzle and hold it with a spanner. Unscrew the nozzle with the other hand.
Tap (no pun intended) the nozzle on a block of wood to free the finned section inside. Remove and replace the combined washer jumper.
Reassemble the tap and test.
Mixer tap spout
If leakage occurs from the base of the spout, the likely cause is a worn seal.
Turn off both taps but not the main supply to them.
Unscrew or lift up the retaining shroud.
Lift the spout up carefully.
On some models, the spout is held in place with a retaining screw, which should be undone.
Remove and replace the worn seal, which is usually an "O" ring type – like a little rubber ring sitting in the groove on the assembly.
Be sure not to damage or stretch the "O" ring when refitting your spout. A little silicone lubricant may be used to ease reassembly.