There is no "good and easy" way to plumb that configuration. There is also no prepackaged setup. The disposer in the middle means that the one sink drain has to go around it. If you know that it will be installed ahead of time, then you can put in a second drain opening for that sink. But, in your case you did not have that luxury. If possible, install a "Y" between the trap and the wall and extend a separate line to the "odd" sink bowl and hook up the other one and the disposer if it were just a double sink. If you do not have that much room, then you are destined to buy alot of slip fittings and tubing and create a "kludge" which jogs around the disposer and connects all three sinks to one trap. In any case it is seldom an elegant looking drain system. If you think yours was heavy, you should try lifting mine. 48" wide with 8" deep bowls.