Plumbing Questions? Ask a Plumbing Expert.
When you ran the hose did you go through the p trap.
Then what you need is to run a snake with a cutter head on it to clear out the roots and this should be a 3/8" cable. Here is a site that will show you what I mean.
Also some times you need a longer tailpice on the drain because the washing machine drains to fast so a longer tailpice will do the trick if the drains are clear.
You should never pour drain cleaner in the drain as they dont work and a snake will.