That is for draining the engine oil without having to climb down in engine compartment to do it. You remove square headed brass plug on the end then let it drain. Make sure to warm the oil up first, and remove the dipstick cap to allow air in. Even then, you should allow for a couple of hours of drain time. These things are notoriously very slow!
Not ever using one before, I trust it is completely sealed around the pipe outlet. Other wise water will get in... And YES there are many other things that could be said about it, but I won't start with anything to get in trouble either! :facepalm:
Is the boat plug wired to the end of it noticed the cable on the end. Not factory but alot easier and cleaner way to change the oil like others said slow but way easier...