If you leave a hose connected to the sewer and connected to your pop up drain, you may get some sewer gas smell from the sink. I assume you don't have a holding tank.
If I'm conencted to a sewer on site with my TT, I never leave the dump valves open. Let the tanks fill up, then dump. This prevents sewer smells from entering and allows for proper dumping/clearing out of the sediment & solid waste in the tanks.
You could collect grey water in a tote or bucket, and dump it down the sewer as needed.