This picture shows the tip sidings in 1988:
https://www.flickr.com/photos/30843245@N00/49511848817/ (Photo: Michael J. Collins)
At this time there were car loading ramps at the east end of the tip sidings (although I think car loading subsequently moved to the other side of the line before ceasing entirely). The shorter sidings on the right are labelled as "Powell Duffryn" on a track diagram (Quail map) from 1988, and I think were probably used to maintain the tank wagons operating from the nearby Carless refinery.
This 2020 drone shot shows a panorama of the yard:
https://www.flickr.com/photos/robmcrorie/50376051682/ (Photo: robmcrorie)
Zooming in shows a track machine in the tip sidings along with the maintenance shed. The shed has been there at least 20 years - it's shown on a 2006 track diagram, with these sidings labelled "EWS" - the shed was possibly originally used for wagon repairs but I'm not sure. More recently, there have been "high output" trains operating from Harwich for Network Rail, but I think these were usually stabled in the main yard near the carriage sidings. There's another more recent maintenance shed visible there.
I think the main current purpose of the tip sidings is for shunting incoming trains of gas condensate over to the Carless refinery.
Here 66783 is seen in the tip sidings after arriving with 6A32 from North Walsham:
https://www.flickr.com/photos/77792219@N08/53090794197/in/photostream/ (Photo: pnb151)
Clicking left on this photo goes through a sequence of shots showing the shunt move into the refinery sidings, which involves splitting the train and a couple of reversals.
The "tip" itself was a siding visible in one of these shots which was a traditional "civil engineers tip" used by British Rail for the disposal of spent ballast (spoil). I think this would have come in on trains from Whitemoor and Temple Mills with material from weekend engineering possessions.
31125 is seen passing Wrabness with a spoil train for Harwich tip in May 1983:
https://www.flickr.com/photos/151904976@N08/25148106457/ (Photo: Michael Hart)
The tip siding was later used for deliveries of stone from the Mendips (a portion from a jumbo working to Acton). It hadn't occurred to me before, but when the high output trains were working from Harwich, I suspect the tip siding may have come back into use as an engineers tip / ballast loading point. This 2018 view shows the tip siding in the distance with a pile of clean stone to the left and what appear to be piles of spoil to the right. There are high output wagons in the main yard, plus 66759 with the North Walsham tanks in the tip sidings:
https://www.flickr.com/photos/138063305@N03/44779740852/ (Photo: Roger Goodrum)
The yard at Harwich is no longer used as a base for the high-output trains, but there is a plan to use it for the Sizewell project - I think the idea is that trains of materials will run to Harwich and then be split into two portions for onward movement to Sizewell.
