When the washer is draining it is making my bathroom sink back up

Have you changed anything lately? Added new plumbing or is this just something that has cropped up recently?

Answering that will help to indentify your problem.

Hi Dlaird

It sounds like the drain line that is common to both the sink and washing machine are clogged and the drain line needs to be snaked to clear the blockage.

You can call a plumber in or rent an electric snake machine (and purchase leather gloves and a pair of safety goggles) and clean the drain yourself.

If you choose to snake the drain, you can look for a cleanout to access the drain pipe, or if your roof is flat enough you may be able to snake through the sink or washing machine vent.

Good luck!

Mark