When the washer drains it sucks the water out of the toilet?

Sounds like your washer doesn't have a connection to your "stack pipe". As water moves through a drain pipe, it creates a vacuum behind it, the "stack pipe" or "vent pipe" is usually a pipe that goes through the roof of your house and provides an open air connection to all of your Plumbing fixtures so the vacuum is provided a way to suck air rather than sucking the water out of your "P" traps or other fixtures such as your toilet.

Chances are your toilet is also "sucking" from your washer, but you just don't notice it.

It is also dangerous because if the washer or other fixtures are sucking water out of your "P" traps, then you may be getting methane and other sewer gases into your house.

Have a pipe run from washer drain to your vent pipe and this should eliminate the problem. Be sure it connects to the vent pipe because if you ever have a sewer backup, the vent system won't allow the gray water to empty into your house through the air pipe.