Yes, you can clear a sewer line with a pressure washer.
Lets take a look at the equipment you need.
First, we need a pressure washer. Something with four to eight gallons per minute at 2500 – 3500 psi will do great. If you are working with a drain clogged food waste, grease or animal fat, the hot water will really help get the drain clear.
Next we need a sewer line. We mount the sewer line on a cart with a reel so we can access the clean outs easily. Sewer line is usually ¼ inch and is more flexible than pressure washer hose.
Then there is the sewer nozzle. The jets spray backwards so the line will be pulled through the pipe by the water pressure. Some nozzles also have a jet going forward to break up obstructions. Other sewer nozzles rotate for a more thorough cleaning.
A foot pedal makes one person operation easier so you can activate the pressure washer while leaving your hands free to guide the hose.
After parking as close to the cleanout as you can, move the cart to the cleanout and hook it up to the pressure washer through either a trigger gun or the foot pedal.
Guide the sewer hose into the pipe then start the pressure washer.
The hose will pull itself down the pipe, just work the hose back and forth until the pipe is clear and clean.
Just that easy. Roll the hoses up and Roll out. Job done.
See how it's done here: https://youtu.be/Rt5Uo_2PLnM