This photograph shows a Stuart Turner displacement lubricator with a drain bucket.
The drain bucket is to catch the condensate when the lubricator is blown down before refilling with oil.
On later steam boats, the lubricators are of a larger type that I supply, with a handy tap sticking out of the side at the bottom. My current lubricators are fully automatic in the way that they feed the oil, this way it is not possible to open the oil feed by accident & prematurely empty the oil reservoir.
The engine in this photograph is a "Reeves Borderer". The boat also had a "Weir" type steam powered boiler feed pump fitted.