Our 2008 2955RL had the gray rank replaced, but I think the tank is smaller than the original. So it fills up faster. So recently, the tank overflowed and I found the source to be where the shower drain empties into the tank. So. Question is can anything be done to reseal it through the cargo bay or does the tank need to be dropped and refit. Does sound like a fun job.
Since you have already discovered the problem it seems likely that you can access the problem. There are rubber fittings you can use to connect the drain/vent lines to the tank.
Take a picture and describe how the pipe is leaking and we can better advise you. Maybe it just came loose or the glue seal broke.
2011 2955RL Reese Sidewinder 5th Airborne
2014 RAM 2500 CD Demco Recon Hitch
4X4 Crew Cab/Short Bed