BarbSee if this chart from Thetford helps you out. I'm not sure what model is in the 2010 2551.www.thetford.com/Portals/0/PDFs/toiletChartREV.pdfSue
I'm planning replacing mind later this summer different model,, I'm getting a high profile with step flush,,,10minutes wow,,,,any problems,,any tips or just easy, good instructions?? Just curiousDavid Sparks2008 PC 2350Houston