Your plumber is probably using a better piece of equipment than you can rent locally, that combined with his experience using this device allows him to do it while you can't--BUT- the plumber should be cleaning the main drain (4 inch line) from a different location. Cleaning the main sewer with only a 1.5" or 2" cleaning head does not do as good a job as accessing it from a 4" clean out plug and using a larger cleaning head. See if a plumber can provide access to the main sewer, this will allow a better cleaning job by you or him. Your problem is either roots in the pipe (which will constantly return) or collapsing pipe (typical of homes built prior to mid 60's using orangeberg pipe). Either conditon will only get worse causuing the need for further cleanings.