How do I tell the size of black, grey, and fresh tanks?

Just google your model number with "specs" at the end and you should be able to fine a brochure. Googled it for my dads 2006 fleetwood wilderness and was able to find the origional brochure. Keystones site even has a spot for previous models, had to look up some specs on our 2010 hideout last year when we were selling it.