I've heard 15-20lbs, I put a bypass regulator (10 to 50lbs) and a gauge in for this year. With the thing screwed down tight I havent seen any more than 20lbs yet, I'm thinking of plugging it off just to see what my max is without it (just for shits and grins). It was a really easy install and I'm sure it doesn't hurt anything. Just run a "T" after your shut off valve and dump it to a through hull.
http://www.***boat.com/image_center/...3112bypass.JPG