The first plumber's in the Universe were the Roman's (lets just say its so!) who following the invasion of Britain circa 55BC (Before Cisterns - sorry!) employed Gradients (and you thought they used slaves) to build numerous BathHouses throughout their domain. Their engineering knowledge allowed water to be moved and utilised for sanitary purposes.
And to the present day Gradients are still employed (unlike 15% of the workforce) to provide water for our all important needs. Technology has been harnessed to facilitate this movement and we ourselves have also moved on as we no longer use lumps of sponge dipped in vinegar to clean our nether regions, instead we use cute puppy dogs wrapped in tissue.
Gradients have another essential role to play although the High Way(man's) Code would disagree!
Driving up the Hannastown Hill from the foothills of the Black Mountain to the Upper Springfield Road allows a car (not my car by the way) to be put in neutral and glide effortlessly for miles to the Monagh Bypass, a saving to the environment and the wallet. Then if traversing in the opposite direction, the user is not only afFORDed a magical view of the Mournes but the flashing warning light indicating petrol tank empty mysteriously disappears and the needle creeps to the tank quarter full mark. To petrol cap it all a noiseless descent down the Hannahstown hill allows the car window to be opened and God's majesty to be revealed - As the Roman Plumber would say about his cistern: "Apparere Quanrantis Cumulatus" - (It appears quarter full) - precious!