There are a number of other issues to repairing cracks in ABS tanks and pipes.
Cracks also need to be enlarged rather than just brushing the patching goop on top of the surface. Usually a crack is opened up to a "V" shape with a knife or file or a dremel tool or similar. This gives much more surface area for the cement to bond to.
Prep the surface by cleaning with acetone.
The cement mixture needs to be applied in light coats to build-up a good bond. Coat it, let it dry overnight, lightly sand (#400 or so), re-coat covering a slightly larger area. Repeat several times until the "V" is filled.
You don't need to purchase expensive patching material. A scrap of ABS and some ABS cement from the plumbing section of your local home improvement store will do the trick. Grind up a bunch of ABS shavings with a rasp or coarse file and then mix with some of the cement. Works great.
A number of my friends over on the Sunline Club have dealt with this issue and written up some good instructions with pictures. For more detail:
http://www.sunlineclub.com/forums/f7...air-10514.html
http://www.sunlineclub.com/forums/f7...ank-10504.html
http://www.sunlineclub.com/forums/f6...1550-8896.html
http://www.sunlineclub.com/forums/f7...ics-10555.html
Given the sheer number of Keystone trailers already manufactured, I would guess that this repair will come up over and over again.
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