I've got a story to tell you. The local RV dealer near me called about a sewer backup. We head over there and open up the manhole in their parking lot. We see that it is almost spilling into the parking lot. I got the clam shovel out to check which way the lines go. I felt something so I clamped onto it. I pulled out a RV discharge hose and it still wouldn't drain. I pulled out another, as to which the line finally opened. When we were done I went to speak with the manager. I asked him how many times they illegaly dump sanitary into the city sewer. He looked at me dumbfounded. I showed him the discharge hoses and he got pissed. I wondered how his employees were dumping without him knowing.
So don't dump in the city sewer. It is illegal and you never know the hose may fall in.
That is interesting. Not only do we have holding tank dump recepticles in two of our service bays, we have a public RV dump station in the parking lot. All is approved by the city of Ishpeming. I know city of Marquete also has two RV dump stations, one for pay use (for non-registered campers) at the city tourist campground, and another you can use for free at the city sewage treatment plant. The later is the closest to me, being only about 2 - 3 miles from the house, plus the price is right.
There is another free one at the sewage treatment plant at the community of K.I. Sawyer (formerly Air Force Base).