I am about to begin getting quote and budgeting for room addition. My house is on a slab. I plan on adding a bathroom and curious If I can tie into the existing bathroom drains? The new bathroom will be about 15 ft away from old bathroom drains. Easiest way to tell if I will have enough fall from new bathroom to existing bathroom? I will be having professional do this obviously but want to be prepared and somewhat understand what can or will need to be done.