The top of the water distribution chamber peeks just above the ground on the Kovacılar Sk, behind a shop called Bal Yuvası.
The Tezgahçılar water distribution chamber was part of the Kırkçeşme/Forty Fountains Waterway. The water passed from the Eğrikapι water distribution chamber at the old historical city walls to Tezgahçılar to the fountains of Kırkçeşme (now demolished and repalced by Atatürk Boulevard, from the 1940s).
Located 25 m below Bozdoğan Kemeri, it has been called a 'completely Roman structure' by Çeçen. However, this is hard to verify; the only thing for certain is that Tezgahçılar is first attested when Sinan reworked the Forty Fountains Waterway (Crow et al., 2008, p. 116).
Also on Google Maps.