I usually remove my pads after I'm done with them and place them in a closed cabinet.
The next time I go to use them, I first clean them on a rotary buffer at the highest RPM setting while running a nylon brush against the surface. This is what works the best for me.
If you don't have a rotary buffer, then here are some more methods. The below was taken from another post that asked about excess product build-up in foam pads after using on the PC
question about product buildup
Build up of product in foam pads when using the PC is a common problem. It could be an indicator that your using too much product, but it also happens just from lots of use.
The problem is that the foam pad is a product originally designed for use with a rotary buffer. The direct drive action of the rotary buffer tends to cause excess product to sling out of the pad because of centrifugal force. The oscillating action of the PC tends to push product up into the foam pad resulting in pad saturation.
One way to remove excess product is to place the foam pad on a rotary buffer and bring the rpms up to the highest speed, this will help to expel the excess product out of the pad. You of course need to own a rotary buffer to do this and you should also do it outside, away from anything you don't want product splatter on.
Another method a friend of mine told me about is to place the foam pad in an absorbent terry cloth towel and the roll the foam pad up into the towel and squeeze it, thus expelling the excess product out of the foam and into the towel. You can also just hold a clean, dry towel into the foam pad and absorb some excess product out of this way.
Another way is to let the foam pad dry, and then tap the foam pad with your hand aggressively, this will knock the dried product out of the pad.
A way to remove excess product that has built up on the surface of the pad is to allow the pad to dry, and then scrape the excess product off the surface of the foam pad using a nylon brush like a toothbrush.
A suggestion for saturated pads is to let them sit upside down on a clean, folded towel so that any excess product in the foam will tend to move towards the towel, out of the foam, versus sitting it up right where the product will migrate to the Velcro backing.
This is a problem for everyone that uses the Porter Cable Dual Action Polisher no matter who's foam pads they use.
Here's another I've read about,
Store wet, upside down in a sealable zip-lock bag is an option that I have heard some people use. This way they don't actually dry out and because they're upside down, your product doesn't soak into the velcro backing. I don't like this method, I don't think it's a recommend method from Meguiar's, I just thought I would pass it on.
Hope this helps...
Mike