Album of the pipe and resulting sludgy mess

I've been in my Chicago home for about 2 years now and only in the past couple weeks did we start noticing a sewage smell sometimes in our back yard. I couldnt pinpoint it at first until we saw our dogs licking at this liquid. You can see in the pics the pvc pipe running from inside their house, along the back of the house to our fenceline.

When I moved our plants and furniture off the fence I saw a pool of foul liquid, and the PVC pipe from our neighbors house was slowly draining that liquid into the gravel between our homes. Unfortunately it doesn't drain anywhere and just pools, sometimes onto our patio and sidewalk.

Not sure if the pipe is new or something just started causing it to discharge this liquid, but its getting worse and my dogs are wanting to lick it if we dont watch over them.

To make it worse, my neighbors, while very polite, speak almost no English. We have gotten along but don't speak too much as the language barrier is pretty strong. Before I try breaching the subject hopefully someone can tell me what I'm looking at here, as I am not sure why someone would have sewage draining from the back of their house in a 3/4" pvc pipe like that.