My stand up drain for my washer comes to a Y at the top actually it has a fitting at the top I think whoever put it in uses it as a vent.but if I want to install a compression fitting at the top so my drain hose from the washer fits tight in it so it doesn't blow out water will I still need that Y at the top or can I cut that one off and glue the compression fitting on

If your washer is overflowing the standpipe, you have bigger issues than the wye. Can you post a pic of your standpipe? We will try to give you the best cure for your problem.