On mine the fresh water tank vent line (not overflow - more on that in a second) and drain line (that one has a valve on it) are directly below the tank. The low-point drains are tucked up near the floor close by. Those have large nuts on them, which need to be unscrewed when draining. I'll probably convert them to valves.
The "overflow" is really the vent line and SHOULD have been routed up through the floor and attached to the vent hole next to the fill spout. I have a thread on this in the Salem sub-forum, most recent post was yesterday so it should be easy to find.
2008 FR Salem 26TBUD
2010 FR R-Pod 171 (2009-2015)
2010 Chevy Suburban
Honda EU3000is inverter-generator