We had our house remodeled 18 months ago. The drywallers may have used the utility sink for more than just water. The sink drain was clogged after words so I successfully snaked it out. Now after some grouting it is clogged again. When I used it to clean up after thinset and grout I would only wash off the tools after washing the heavy stuff outdoors. I ran the water much.
Anyway, is there a known way of removing the blockage ? It is a 3" cast iron pipe.
The clog is probably in the trap. The plaster and sand would settle there. Try removing the trap -- it may be easier to just replace it rather than clean it.
To really stop up a trap, I once ran crab leg shells through the disposer. They don't float. They got no farther than the trap and it locked up solid.
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