The location of the actual washdown fixture and the location of the fresh water pump makes a difference. For example if you want the washdown aft and the pump is under the deck near the cabin, the job will be harder then if the pump were located aft.
The washdown fixture has to be connected using a tee fitting somewhere in the output side of the wash down pump. The design is pretty simple, the im[implementation may not be as easy if the pump is hard to get to.