Methods and assemblies for cleaning a control rod guide tube in a nuclear reactor are described. An assembly, in accordance with one embodiment, includes a support housing and a flush tube. The support housing includes a bore extending between its first and second ends. The flush tube also includes a bore extending between its first and second ends. The flush tube extends through the support housing bore and is movably coupled to the support housing adjacent the first end of the support housing. The second end of the flush tube extends from the support housing and includes a flush nozzle which is movable between a first, or latched, position and a second, or open, position.