Which of These Pipes is the Cylinder Feed Connection? Drainage and wastage systems and plumbing help, advice and answers

[TheRockstar]

I’m currenty taking on the task of de scaling the heating system in my house with Fernox D3. As directed, I need to funnel the solution into cylinder feed connection inside the cold Water Storage tank in my loft. I think I have a sneaky idea which pipe it may be, but which of the pipes is the one I need to funnel the solution into?

Thanks!