If I pour mineral oil down the sewer trap will that stop the sewer gases from coming back up into our building?

Not mineral water, but cooking oil can help. I'm assuming that you have a drain in the basement floor that is almost never used, and consequently all the water that is supposed to be in the trap evaporated away, leaving nothing to block the sewer gasses from coming out. Same thing can happen with any bath fixture that is rarely used (a guest room shower, for example). You can pour water into the drain and that will stop the problem, at least temporarily until the water evaporates again in a few weeks. If you pour cooking oil that will also stop the problem, and cooking oil doesn't evaporate so it's a much longer term fix. It only requres about a cup. The downside to using cooking oil versus water is that it's lighter than water, so if the drain is used for water the cooking oil is llikely to come up out of the drain and make the floor slippery - so you should not use this trick in the guiest room shower!

Poster said "mineral oil ".

Mineral oil is just fine. You could also purchase a trapguard and install that... check it out @

Trap Guard – The Trap Primer Alternative

Mark

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If I pour mineral oil down the sewer trap will that stop the sewer gases from coming back up into our building?

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What type of trap are we talking about> A running trap in the sewer line to the street? A fixture trap? Is this trap used or is it simply setting there unused? Back to you, Tom