Jim, I own a 1997 challenger with a single 787. There is no cap on the transom end. It only has a cap on a chain under the deck lid. The one on the rear is for overflow of water when it is on the hose. You can hook up the hose to the seadoo and have them run for up to 5 minutes. Connect the hose and start the seadoo. Turn on the water after it is started. Turn off the water, than shut down the seadoo. This way it won't allow water to back flow into the engine through the exhaust due to no back pressure from the engine not running. The bearings and seals on the impeller jet pump are cooled from being in the water. When it is on the trailer it doesn't have that cooling effect so they will get hot after about 5 minutes.
I pre start my seadoo's too, dry before I leave for the launch too. Just for a second or 2 to be sure it will start at launch. Peace of mind is worth lot.
I hope this helps you out.
Karl
