[wingnut60]

Do the best you can to follow the two drain lines back into the frame area. In every trailer I have had, there is a valve with a pull cable somewhere in the lines. This may mean taking off some of the covering or the box I see in the lower pic.
Since this is a used unit, there is no telling how the previous owner handled or modified the system.
Since you are going to have it situated permanently, you will have to learn NOT to have the black (sewer) tank valve left open--there must be fluid in the tank, or ugly solids will build up. Use the tank til it is near full, then dump and flush--this is a really dirty side of RV life, but necessary.
Keep working at this, and ask questions anytime.
Joe