With all the cats here, this is what I did:

1. Removed the air intake registers, used the vacuum an dput the hose down as far as possible, moving it side to side

2. Put some filter material on the INSIDE of the register before replacing it. I used paper clips, binder clips, and duct tape to hold it in place.

That was soon after I bought the house, 6 years ago or so. Since then, I just vacuum the front grill on ALL the registers, in and output ones alike.