You mean like this?
Well that means it's probably thin-wall PVC, used on houses as guttering. It's thinner then DWV and I would not personally use it for that reason.
If you are building a combustion, try and use thicker PVC pipe and fittings, DWV should be fine but there is a chance it could explode. In that case you'll need to use pressure rated parts.
In a pneumatic or 'advanced combustion' (uses metered propane or MAPP) I would recommend to never, ever use DWV PVC. DWV isn't pressure rated, meaning it's never been pressure tested and you'll never know how low of a pressure it could blow up at.
Here's an article on how-to identify pressure rated PVC:
http://www.spudfiles.com/spud_wiki/inde ... _Rated_PVC