Will oil or powdered cement do more damage to pipes?

In what ways, Powdered cement if it gets wet and dries in pipe will not be able often to be cleaned out, Oil normally if it becomes solid, will desolve in hot water and/or be able to be cleaned out

They will not damage a pipe per se but can cause the pipe to no longer drain properly. Nothing should go down your sewer drain that will not biodegrade. Cement can harden underwater, did you know that?

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Will oil or powdered cement do more damage to pipes?

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This question's a no-brainjer. Oil will flow through the pipes while powdered cement will harden up and block the pipe as soon as moisture hits it. Cheers, Tom