Hayward SP710

[waste]

Steve#1, welcome to the forum! A quick way to stop it is to not run the pump . However, that's a bad choice, as you want the pool water to circulate when, as long as the pool isn't closed for the winter.
As a 'stop gap measure', you can either put a valve on it, as AL suggested, or plug it when you're not backwashing or wasting (there are a couple of ways to do this, depending on how the backwash is plumbed, though the simplest is to unscrew the backwash adaptor and put in a SP 1022-C 1 1/2" threaded plug w/ O-ring). There is something wrong on the inside of the valve - it could be a torn or 'buckled' 'spider gasket' (aka wagon wheel) or a broken 'channel' that seats the gasket. The thread Al alluded to is http://www.poolforum.com/pf2/showthread.php?t=1331. Give it a read and see if the advice there fits your situation.
When you're ready to take a look inside the multi-port, use a #3 Phillips-head screwdriver to remove the 8 screws (keep your hand under the locknuts, so you don't loose them). The top has a notched edge on one side, so as long as you match that up, you'll be able to reassemble it in the correct position, if you need a new gasket the part # is SP 710- D - if the channels in the bottom part of the MP are cracked or a section is missing, you need to get a SP 710 [u]R[/] body for it - the "r" designates that it's for a DE filter.
I hope that Ive properly explained how to see if the valve itself is broken, (while I was looking up the link to what Al said, I came across a thread which tells you how to proporly backwash your filter, http://www.poolforum.com/pf2/showthread.php?t=3613 - post #6.
I welcome you again to the forum, should you ever need any help with your pool, please ask us!, and we'll help you as much as we can (and that covers just about everything )

[Steve #1]

Thanks for the tips guys. For now I just have the pump off. I've run it a few times then added water just to circulate some chlorine.

I picked up a plug but havn't had a chance to do anything with it. I think I'm going to pull the valve apart and see what the inside looks like (stand by for my "where does this piece go " thread). I've been trying to get finished moving and tomorrow is my last day so maybe then I'll have a chance to tackle this issue.

[Steve #1]

Update: I had a chance to look at it Sunday (finely finished moving). The gasket was mangled. I was expecting pieces to go everywhere when I took it apart and was surprised by how simple it was. Removed the silicone that had held the old gasket in, cleaned it up super glued the new one in.. put a little lube on it and put the screws back in. Took less than an hour which included drying time, picking up the gasket, and hitting the grocery store for milk.

Thanks for the help guys!

[Poconos]

Glad it worked out. Yeah...nothing flys apart. One thing to remember though, absolutely never change positions when the pump is on or you'll mangle another one as I did my first one. And, after you kill the pump make sure water has stabilized and stopped flowing before moving the handle.
Al