Vent pipe into cws in attic

[Joef]

So the cws in the attic needs to be moved a few metres. Is it ok to run the vent pipe across from the existing pipe work with a slight rise to where the new position of the cws is?
Please tell me what the best practice is here?

 

[Best]

Yes, it is fine to extend the cwt vent pipe. It has to be a minimum height above tank. There is a formula for this.

Just be sure to give the pipe a constant rise before dropping down into tank.
I would advise to use copper because plastic used as a vent pipe is very prone to being accidentally pulled out of tank and could cause a flood.
Clip and insulate pipe.