balfre1946....."Dale.Traveling" really gave you the best suggestion. If the hole saw plug is in there and you can prove it, Fleetwood may be very willing to step up and fix the issue.
My 2004 Fleetwood Fiesta 32' had a terrible black tank design. I was unable to determine this until I brought home a fiber optic camera and went down the toilet opening. They had installed a tank where the waste fell onto an angled shelf and then was suppose to slide into the main tank.....didn't work! They finally did a recall on the tank after I sold it.
Don & Mary
2014 Newmar Dutch Star 4018
2012 Chevrolet Silverado LTZ CrewCab 4WD
2013 Polaris RZR 800 LE
Think you might have one of those cutout problems. They can show up the first week or years later.
I think Jim's comment is your problem. Since your coach is fairly new (2010) I'm more inclined to suspect the cut out fell back into the tank during construction and is now blocking the drain.
For a bit of education - the builder will use a Hole Saw to drill the various holes in the tank for the lines feeding the tank and draining. A hole saw will cut a disk that is about an 1/8" smaller then the actual hole size. The 1/8" is the width of the saw blade. Normally the disk will stay in the saw but sometimes it falls into the tank. If the builder neglects to remove the disk over time it will find its way to the drain and slow draining to a trickle.
Now the bad news. If this is your problem there isn't a simple solution. Since the drain is normally the largest hole in the tank the disk is too big to get out by any other route. What complicates the problem is the disk is probably bigger than the drain lines.
What I would recommend is contact a plumber who has a fiber optic camera they use to inspect sewer lines. Don't need an RV plumber for this. They can either come up thru the tank drain line or thru one of the feed lines and inspect the interior of the tank. If the cut out disk is present get a hard copy picture and call Fleetwood to negotiate a workmanship claim for repair.
Also you could try back flushing the tank with a Hydroflush valve with will push any obstruction back into the tank.
2006 Hurricane 31D aka 'Moby' the Whale
FCC(SW) US Navy Retired 1980-2003
Stella my Navigator
Bogart the All American RV Dog
Cocoui waiting for me at the Rainbow Bridge