If you have only one line comming from your pump you would attach this to the bottom of the manifold (if two lines from pump, connect one to each side of manifold). This water ends up at the head, if you have only one line attached to your manifold you would leave one of the two outlets capped on the head and the other available outlet to the bottom of the headpipe (the piece that says "Factory Pipe". The water will end up coming out from the top pipe at this point, from here you will want to dump overboard, BUT you must use a 'T' to divert some water into the end of the pipe near the waterbox. Ideally you would want a the water going through the 'T' so the majority of the water goes overboard via the pisser and the leg of the 'T' gets dumped at the stinger (tip of pipe).
If you have Dual cooling in place (two lines from pump) take the cap off of the second outlet from the head and dump that overboard through another pisser.
Search and you will find plenty of diagrams....