Lawrence -
First, I must state our coaches are one year apart - yours a 2003, ours a 2004, and different models - yours a Monterey Newport, ours a Marquis Sapphire.
Be that as it may be, our two waste tanks are located in the basement storage bay immediately aft of the water pump, inverter, etc. and fore of the dual axle. Access to the two waste tanks can be made from either side of the coach through basement doors. The "working" side of the two waste tanks is accessed through the water bay door on the street side of the coach. Behind that door, you should find several electric switches and/or dump gate handles for dumping the tanks, and electric switches for the fresh water tank fill and knobs to turn on/off both hot/cold water to various devices in the living quarters of the coach such as faucets, shower, toilet, washer/dryer, etc. The stainless steel plate where all the switches and gates are attached is removable by unscrewing several screws - 10 or 12 screws - and pulling the plate out. The plate will tip out at the top so that you can see down to the two waste tank drain valves. The problem is the hot/cold water on/off knobs are attached to a manifold on the back of the stainless steel plate. To get better access to those things behind the plate you have to remove the water manifold. That is a PITA but must be done to get free access.
http://beaveramb.org/forum/index.php/topic,6981.msg50054.html#msg50054http://beaveramb.org/forum/index.php/topic,5153.msg38508.html#msg38508On the other side of the coach, the curbside, there is also a door - without a handle to open it - to access the other end of the two waste tanks. This door is attached at its bottom under the door with two quick release brackets. Release the two brackets and the door will lift similarly to the other basement bay doors.
