How to fix leaking fitting under sink?

[Tywoodpk]

I discovered the fitting under my sink is leaking.  It’s a drip from the brass fitting where the arrow is pointing in the picture.   
it only leaks when running the tap. 
Is this something I can replace myself or somehow stop the leak or do I need to get a plumber? 
I’m not sure what the grey thing is to the right, but that goes down to the dishwasher, I think.  The copper pipe sticking up goes nowhere,  so I’m not sure why it’s there or what it does. 
thanks in advance for any help or suggestions. 

[JDE]

Tywoodpk

This whole set up is just to get water to your dishwasher. The pipe going up is a antihammer device. It could be put anywhere. The grey piece would be the pressure regulator for the dishwasher. In order I would try 1. Tightening up nut where dripping. 2. Switch off water with tap immediately next to it, check rubber washer inside and replace it (plumbing section Bunnings) and use some plumbing tape on thread. Or you could  try just unscrewing it putting some plumbers tape on thread and screwing back up. Or remove whole centre section and screw grey part directly to tap, this will remove the hammer arestor and may cause hammering but arestor can be put elsewhere. Most houses do not have an arestor unless water pressure is really high.

JDE

[MitchellMc]

Hi @Tywoodpk,

It's great to see that @JDE has already provided some helpful advice. Regarding whether you can do this yourself, this is considered plumbing work and requires a plumber to complete it for you. It might be worth double-checking regulations in your area, but typically, unless it's a tap washer, shower head swap or irrigation pipes, it's considered plumbing work, so you'll need a plumber.

Please let us know if you have any questions.

Mitchell

[Tywoodpk]

Thank you.   I did go to Bunnings this morning and the lovely gentleman there pointed out exactly the same thing. He also explained the multiple things that could possibly go wrong with me trying to do it myself. So I shall contact a plumber on Monday and get him to come out

Many thanks for your advice.