I have heard of the 3rd handle somewhere along the frame near the tire. Sounds like you can't find it because it fell off during delivery from the manufacturer to the dealer. This has happened to others on this forum and they have remedied that in one fashion or another. And since your dealer didn't see it, they apparently assumed one gray handle dumps both tanks (this is only true on PT's TT's). If you look along the frame for a slot or hole, then pull down the underbelly cover in that area, you'll probably find the elusive valve.........Good luck.