One side of the Drain Assembly is threaded so it will screw into the .75 inch Threaded Seal opening. (The image below is for illustrative purposes only. In the Add to Cart section at the bottom of the page you are only purchasing the Drain Assembly as shown in the above image).
The opposite end of the Drain Assembly has the same thread size as a normal garden hose. That end will come with a cap screwed on to it.
Carefully screw the Drain Assembly into the Threaded Seal ( hold the 'tab' of the Threaded Seal so it does not spin while screwing in the Drain Assembly. )
The Drain Assembly is at position #4 in the drawing below.