According to my wife, my Maytag washer, during the Rinse cycle, tries to
fill the tub with water, but it drains out as quickly as it enters. It
never proceeds beyond this point when the problem occurs.

Unfortunately, this problem only shows up once every month or so, and every
time I try to provoke this problem or witness this, the machine runs fine.
Since she does about 5 loads a week of laundry, this failure only occurs
roughly 5% of the time, and is hard to trouble-shoot.

Is there a solenoid or timer-controlled valve which is closed to prevent
drainage during the Rinse cycle on most washers? Or is the empytying of the
tub merely controlled by the pump which is only activated when it is needed
to empty the tub after the Rinse process has been completed? My impression
is that the draining is not just done by gravity but by pumping when the
drum is being spun. My wife says the water just drains out even if there is
no spin taking place.

I have tried to find a complete schematic but have not found one searching
with Google and searching some appliance parts sites.

Any suggestions would be very much appreciated.