The back panel will not come off of this washer to access the drain hose connection to the drain pump. You need to
unplug the washer
and remove the front panel to access this drain hose connection. I provided a procedure for accessing (and replacing) the drain pump in the image below. Before removing the drain line from the pump, be sure that you drain the washer. You can use a wet/dry shop vacuum if you have one. Be prepared to catch residual water from the drain line hoses when you remove them from the pump. If you find no clogs or restrictions in the drain lines, then you may need to replace the drain pump.
You can order parts from the
website if necessary.
This information should help you troubleshoot and fix your washer drain problem. If you need more help, resubmit your question with additional details.