In Blender, you can texture or weight paint on just the front faces, or on all the faces underneath the cursor. This second option allows you to paint the front and back of an object at the same time. It's fairly simple to do this- all you have to do is turn off two checkboxes in the Header:
You may still run into issues trying to paint the top or bottom of your object- if a face is mostly flat compared to the view, it won't paint. This can leave a nasty-looking smeared effect and gaps in your painting. Fortunately, it's easy to fix this.
There's another checkbox you'll want to turn off, this one in the Falloff menu: