If the tank is black, odds are high it is ABS like most all of the other Sunlines.
See these threads on ABS tank repair. While some of them may be the black tank leaking, the gray tank is made the same way and the fittings are from the same material too.
And if you need more, try this Google Custom Search our Admin made for our site. It works much better then the embedded search tool on the forum.
Scroll down to the "Google Custom Search" box below the main one. Put in "ABS repair" and hit go. It will find all threads with those words and much more.
Hope this helps and good luck. Let us know how you make out so we can add your repair to the list
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
Google Custom Search For Sunline Owners Club