That’s encouraging, and sounds like he is planning to include a leveler. The levelers I’m familiar with are simple buckets that look like the skimmer and have a float valve tied to your house water supply. The entire install may not exactly be cheap, as a plumber has to install a T at an existing hose bib and a back flow preventer to run water to the float, which then opens and equalized the water if the pool level drops too low. The drain line is another piece of pipe level with the maximum desired water line, and it does indeed need to run that excess water out to a sewer or storm drain. There are city guidelines to consider regarding where you are allowed to drain. If he’s already included that setup in your price, so much the better!