Basement shower drain help...

I could use some more advice with installing this p-trap...

Is there a certain length for the inlet pipe into the p-trap, should it be long enough to hold enough water to push through the trap?

Is it ok to backfill around this pipe (ABS) with sand?

How do I get a downward slope with my piping?

Thanks for the help... see attached pictures

Where are you trying to tie this p-trap into?

The fixture outlet (the piece going into the trap) usually doesn't have a minimum length because it's really irrelevant. You're amost forced to make it atleast 4" long in most cases.

If you're trying to tie that p-trap into the existing pipe in the hole in the trench there then you shouldn't do that. You'll be creating yourself a nice little s-trap (the fall exceeds the diameter of the pipe before you hit a vent).

The trap outlet needs to be at grade with the horizontal drainage in the ground.

You want to do this: