No holding tank?

With a straightforward bog-to-seacock pipe it’s probably best to disconnect it, bash it about a bit to loosen the crud and then finish off by drawing a bottle brush through the pipe from end to end. It may also be filled with descaler by taping up one end using some plastic and gaffer tape.

Removal of the pipe might be avoided by pouring descaler into a vented loop if one is incorporated in the pipeline.

Drop a line through the pipe and use it to draw a bottle brush back and forth