It would have been nice if they had put a couple of handles on that lid.
Septic tanks for the most part don't plug up for years. As long as the bacteria is alive and well, they do a great job of taking care of solids. If the tank is backing up, it may be a drain field problem.
I think the tank cleaner guy is going to like that large hole so he can get the hose in and clean the entire tank. A small hole might restrict his ability to get all the goodies out.