We plugged the hole until we get the replacement part (this week). There is an air release valve on the top also, so we should be safe for a short time period.

Anyway, thanks for the help.[/QUOTE]
To clarify for all above posters, the unit in question is the 'old style' or bump DE filter (Hayward's E-C series). There is no multiport valve, only an inlet at the bottom, outlet (return) on the top and a drain valve on the bottom, opposite the inlet. Therein lays a key difference between sand filters and DE filters, sand filters from the top down - DE from the bottom up. (For y'all with multiports, go look at a friends' pool with a sand filter - you'll notice that the multiport 'settings' - filter/ backwash- are 180 deg reversed). Cleaning this unit involves shutting off the system, releiving the filter pressure and pumping a handle on the top of the unit to 'mix up' the DE & crap (the DE is only coated with 'crap' at it's surface), when you restart the pump, the pressure has magically dropped without backwashing, nor loosing a drop of water. True cleaning has been dicussed elsewhere.
http://www.poolforum.com/pf2/showthread.php?p=1671

HooStat; you don't have a Hayward filter, but I have no idea who made yours. An air relief tube at the bottom doesn't make sense as air rises in water. However, my advice remains the same; clean and check the entire grid assembly for cracks or holes when you have it open to replace the air relief stem. BTW, if cya granuals went through the hole, you can bet that a lot of DE will go through the same hole when you charge the filter or bump it.
(this is my first attempt to provide a link, hope it works )