I'm in the process of redoing kitchen. Countertops are ordered, have new sink and want to clean up this cluster of piped under sink. I'm currently on septic. The guy originally had a modular home on this foundation and had a home built and set on the foundation. He retrofit allot of stuff to fit the newer house including the furnace which had built replaced already. Do I need both sink drains or can I tee then together? There is a disposal and dishwasher. Would also like to put an Oatey vent on there too assist with drain.