Re: toilet rough in
You can certainly use a 12", but there will be a large gap between the back of the tank and the wall. If that doesn't bother you, go for it.
Just make sure the tank is bolted securely to the bowl so it doesn't wiggle around, but don't tighten the bolts beyond that point or you'll crack it.
When installing the tank-to-bowl bolts, there should only be a rubber washer between the bolt head and the porcelain (inside the tank). Installing a metal washer inside the tank will result in leakage.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.