1- Once you get your trap set up, shovel enough materiel onto the skid plate to fill the trap. Once filled, step back and see what the materiel is doing inside the trap. If it blowing the materiel out in a U shaped pattern, you need to elevate the front end a bit.
"Remember, it's not length, it's water velocity... It will vary from location to location."
2- No Classification Required.
3- Before doing a clean out, be sure to block off water flow to the skid plate, which is the top section you shovel onto. There is no need to block off the scoop plate / bottom section.
Always remember to block the water flow on the skid plate before doing a cleanout. There is no need to block off the scoop plate.