Masticator is the culverted section of the Meanwood Beck on its journey through Leeds city to its confluence with the River Aire.
I explored this drain with ConcreteJungle. Check out his blog here!
Along the way, the construction styles, materials and size of this drain change many times.
Towards the downstream end is a CSO chamber containing an Archimedes' screw which is used as a debris screen for a sewer which runs parallel to the Beck.
This, I believe, is where the name of this drain originates.
Anyway, on with the pics...