Originally Posted by speedball1
If you have snaked and cleared out the drain line then there's nothing more you can do to it. And, yes, a trap's necessary. It protects your home from sewer gas escaping. You have two options here. you can do what another asker did and get the manufacture to replace the washer with a less powerful pump, or, you can do what I did when I had the same problem.
I took a 2" female compression fitting, (see image) and glued it on the stand pipe. The hose went into the compression fitting and was tightened down making a water tight connection. The pump will then have to force the discharge through the drain pipe and not out the top of the stand pipe. good luck in whatever you decide. Tom