The Egg is a Victorian storm relief sewer that serves both the River Tyburn (KSP sewer) and the Westbourne (Ranelagh sewer). It begins as the overflow pipe for a hot and humid CSO towards the lower reaches of the Tyburn.
A 15 minute walk downstream leads to the overflow with the Westbourne (and by connection to the Mid Level), here the Egg expands to accommodate the increased flow.
Eventually we came to a remotely controlled gate, when closed it turns the Egg into a storage pipe.
The lower reaches will have to wait for another day.