I wouldn't do a grav bong with salvia. The smoke can be a touch rough, so it's better to use a piece that a) filters through water (a gravity bong doesn't do that) and b) allows you to take the hit slower than a gravity bong would.

I recommend a bubbler or small bong, or even a spoon bowl-- anything but a gravity bong or a joint, actually.

Lateralus, you don't need to worry about corrupting your piece. When you're done smoking the salvia, just give your bowl a quick rinse in the sink, dry it off, and then smoke away!