Imagine a Coke Freestyle Machine that only serves seltzer, but instead of plastic cups you have 2 glasses. This machine is a vending machine that's just installed on the street. There is nowhere to wash the glasses.
This is an older design, but it shows the glasses well.
This is the "classic" design that's Sovietana
This is a modernized replica that you'd use with paper cups
The example machines in the first picture are type AT-101 SM which meant they had the glass rinser which is true. The problem? No soap. So you'd often find lipstick on the glasses, not really a "wash".
But the risk of infection is minimal and nobody really got sick from them in any noticeable way, it's just icky. Drunks stole the glasses all the time tho.
Here's a museum talking about the soda machine inside of the GES-2 power plant.