The Indus Dictionary Project
In this pictograph, tapered chutes feed waste water into a corbelled arch drain.
Harappa: Pottery Body reworked: H-2548 A: Asko Parpola, B. M. Pande, and Petteri Koskikallio, 2010: Corpus of Indus Seals and Inscriptions: Volume 3,1: Page 351: New material, untraced objects, and collections outside India and Pakistan: Suomalainen Tiedeakatemia.
You should note that the photograph of H-2548 in the Corpus is upside down. The inscription begins with a pictograph of the piece of pottery.
Jonathan Kenoyer states that such drains were large enough for workmen to enter and clear any obstructions¹. Inscription H-2548 may therefore, refer to an entry point for workmen, in other words a manhole.
Corbelled Arch Drain: Lynn Fawcett, 2020.
1. Jonathan Mark Kenoyer: HR Area, Corbelled Arch Drain: Harappa.com: https://www.harappa.com/indus6/mohenjodaroHR49.html: Accessed: 10 April 2020.