Gerald,
      Jane tells me we have a lot of smelly water in the basement, after she did a load of laundry. The gray water tank was quite full.  Do we have an overflow pipe on the 2000 Marquis?
  

I don't know about the Marquis, but on a 2000 Thunder the grey overflow is the shower!  

Same here, 2000 Patriot is the shower!!

If the smell and actual water was in the basement, you'd better check all your tank and drain pipe fittings, including under the shower;  there should be an access panel in the front of the shower base where you can at least do a flashlight examination of that section.

Joel

Joel and Randy,
  thanks for the feedback.  Now I have to take the wall down to find out where the grey water came from.  

Ours leaks around the fitting where the vent goes into the tank.  The fitting appears to have been installed crooked at the factory.  The repair looks to be difficult at best.  Our solution is to not over fill the grey tank.

Use of the washer can make for unscheduled over fills.  Although the washer drains into the grey tank in our coach just as yours seems to, the owner's manual appears to indicate that it should not do so.  The way we read it, the washer should drain into the outlet manifold of the sewer drain.  The washer would then not be usable unless the coach is hooked to a sewer.  Perhaps that is a better design or, in our case, a good rule.

I actually have a grey water overflow alarm.  It goes:

DICK, GET IN HERE RIGHT NOW!!!!!

it's repeated constantly until the situation is corrected.  Somehow the alarm is connected to the kitchen as hot meals are delayed for several days.

Jeremy,
There is no gray water overflow on your coach. The gray tank will back-up, and fill the shower as the lowest point in the system.

Your washing machine does not drain into your gray tank. However it drains directly into your sewer outlet unless someone has changed the drain from the original factory design. So if your were hocked up to a sewer system your washer drained directly into it. If you were not hooked up to a sewer system, your washer overflowed at the washing machine drain and flooded the basement.

Gerald

On our 2001 Marquis, the washer drains to the gray tank.  If the gray tank is empty when we start, the 3rd load will overflow.  I estimate the washer uses about 26 gallons per wash.  It is best to be hooked up for that 3rd load, or live with the consequences.  If your washer is not connected to the gray tank, always have the sewer hooked up to use the washer.

Larry

My owner's manual states that the washer drains directly, but I know from experience   that it backs up into the shower.  

The most unpredictable aspect of using the washer/dryer is the fact that the unvented dryer uses water at a rate of ~2.5 gal/hr during the drying cycle.  The water is used on the condensing drum. So 2 hours of drying uses 5 gallons in addition to the wash water.