Pressure washer lube

As a general question, do you have to lube, change oil or what ever to the pressure washer pump itself. If it is model specific, I can add details. It is a Generac, honda engine and an after market pump. It is a horizontal shaft engine, pump mounts to the back. (not under)

 

I've seen recommendations to change every year. I have a Honda engine with a Cat pump and I change mine every other year. I use oil specially for a Cat pump.

 

The replacement pump was B&S Kit 193476GS. I removed it and looked all over for a oil fill/drain plug. Nothing apparent to me. There is a black pressure relief stem (looks like a chimney) that once I removed it, appeared to be wet with oil. Drained it, about a teaspoon full. Tried to refill, took about 2 teaspoon's full to reach the top (green washer). Mounted the pump back on the engine, pulled the cord several times, the oil level did not change. There is a black plastic plug, hex fitting in middle, not sure if I want to remove that?? (springs, ball bearings etc) Appreciate any help.

 

Took some time, but finally got to a B&S rep. She said 75w/90 synthetic oil. The black plug with the hex in the middle was the place for the oil. My local B&S guy said 10-30 non detergent, another mower dealer said straight 30W.