There is a long, thin, rubber-y line wrapped around/connected to the water line pictured below.
Other angle:
The piece in question is loosely hanging via a zip tie on my main water line about shoulder height and can be moved up/down easily.
This can get very far out of whack if you’re using a lot of water outdoors (filling up a swimming pool, watering your garden, washing your car, pressure washing for outdoor cleanup, etc).
For the pool you can generally inform the water/sewer department(s) of that and request an exemption. They'll usually use your average water consumption as your sewer bill for that month.
For ongoing usage that doesn't enter the sewer, such as irrigation, you can often request a second meter be installed, for which sewage isn't billed.