The other mechanics are happy to let them do it. Because of this you will have only 2 or 3 mechanics that work on these systems at any one airport. No one pays much attention to these guys and no mechanic socializes with another mechanic who only works on the waste systems. In fact I had never thought much about this situation until last month...
One day last month I was called out from our base to work on a plane for another airline. When I got the call the dispatcher did not know what the problem was. When I got to the plane I found out that the problem was in waste the disposal system. There was nothing for me to do but to crawl in and fix the problem. When I got into the bay I realized that something was not right. There were more tanks, pumps, and pipes then should have been there. At first I assumed that the system had been changed. It had been 10 years since I had worked on one. As I tried to find the problem I quickly realized the extra piping and tanks were not connected to the waste disposal system. I had just discovered this when another mechanic from my company showed up. It was one of the mechanics who usually works on these systems. I happily turned the job over to him. As I was leaving I asked him about the extra equipment. He told me to "worry about my end of the plane and let him worry about his!"
Full story...
Operation Cloverleaf - backup for the mechanic's story