Related question. Do the toilets get emptied at Euston? And does the train get refuelled at Euston?
Unfortunately, trains are neither 'tanked' or refuelled at terminii, all of these tasks are carried out in depots either overnight or between the peaks, depending on how hard the stock is worked. The process of emptying controlled emission tank involves someone attaching a hose to the tank before then switching on a large pump to empty the tank into a storage tank before being taken away for further processing. Occasionally, some of the tank's contents fail to get into the storage tank, which is one reason that tanking isn't done at terminii. One of the other reasons is the lack of space at terminii. You can't really put the pumps on the platform because of the smell, the irregular positioning of tank valves, as well as taking up space and posing potential trip hazards with hoses running across the platform. You can't put them between the tracks because of the lack of space!
Similar really for refuelling, no space at terminii for either the pumps or the tanks, and fortunately, no real need as trains are *usually* able to run their day's work on 1 fuelling