Welcome He-hoo
I do not know of a direct replacement tank that small. If you have not found the Icon site, see here, again some that are close. I have bought from them, they are a good company with good products. They will custom make things too. Not sure on the cost of custom though
https://www.icondirect.com/waste-hol...atured&page=11
I have had success dealing with ABS plastics and tank cracks, with recently adding fiberglass screen into the ABS cement. The 3" dump area sounds like it is out in the open, the tank vent pipe, that sounds like it may be buried on top where you cannot access it.
If you can get the tank down in the open to deal with the vent pipe, a solvent weld repair may be possible. The cost to repair is low (~ less the $20 to $25) so you do not have a lot to loose if it does not work, but I feel it has a fighting chance, pending what the tank cracks look like.
See these threads for some help on ABS repair.
This one has links to other posts with info
https://www.sunlineclub.com/forums/f...tml#post151851
One on using Plastimend to repair a big hole.
https://www.sunlineclub.com/forums/f...air-14865.html
The plastimend site to call
https://new.plasti-mend.com/
And a recent one on a tank crack.
https://www.sunlineclub.com/forums/f...val-20112.html
Hope this helps and let us know how you make out.
John
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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
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