The back-pumping system which appears to have been employed at Rowley Bottom was far from straightforward.
Locks 20 - 22 had been built in a line towards Midford, which put the lower level of the canal a long distance from the upper level to which the water needed to be returned. There was no possibility of extending the upper level eastwards; and to extend the lower level westwards as a canal would have reqiured vast and expensive tunneling. The alternative of a cheaper-to-build underground adit, about 2ft wide, from the foot of Lock 22 to the engine site would have needed a slope of around 1:40 in order to ensure adequate flow rates. This would have put the bottom of the engine well at a great depth and increased the cost of pumping. As the bottom three locks were already supplied with water from the Cam Brook, this was the solution to the problem.

The Lower Reach, at the bottom of the inclined plane, was cut off from Lock 19 but continued to be fed from the brook. (1) An undergroung adit was constructed from there to the base of the engine pump well (2) (this has recently come to light). The engine pumped the water up (3)(4) to the Upper Reach (5) from where it entered the lock flight at Lock 1. (6)
After descending the lock flight, (7) it was returned to the Cam Brook below Lock 22. (8)