Baking Soda and vinegar if you have access. If you use bleach be careful not to use hot water for awhile. The bleach ends up sitting in the u-pipe and when mixed with hot water it can create toxic fumes that can make your crew sick/high. If you let it sit, make sure to flush the pipes good with cool water for awhile after. The manure could be a gas smell from the sewer system.

Using gloves, bleach the fuck out of your drain. I'm talking the drain covers, the drain itself, and wash some bleach down the sink for good measure. Also make sure the floor around the drain is clean as well. It won't fix it immediately but it should help at least.

Could it be your grease trap? Lots of stores have them outside but when it’s indoors, every store I’ve been at, it’s near the sink.