Sewer Pipe leak from kitchen sink to gray tank

[rcrab]

Hey,  Need to know how to get to the sewer pipe on a 89 Itasca 27 RT Sun Flyer queen island bed formation. The gray water from sink goes from side door across to Gray water tank.  It seems to leak right in the middle and not a small leak.  I see no access points.  I have a furnace in line with the pipe I think.  Just Gray tank on drivers side.  Is there a joint in that area? Can I line it some how? The rest of the system is ok.  Just the kitchen sink to gray tank.
R Crab
Billings, Mt