WOW, thanks a ton bondebond. This is exactly the information I was looking for. I have not been able to spend much time looking at the new trailer but I did take a look under it and saw the line from the sink to the drain, no holding tank to be found.
I will start researching holding tanks in hopes that we can add one. I do know that they come in many sizes and shapes.
I noticed that you have added a cap that has the garden hose outlet incorporated. This is what I use on my trailer when we are in a place where it is acceptable to drain gray water into the surrounding bushes. Do you see any problems with doing this?