try it wet. use a hose with a fine mist in one hand and the block in the other. the runoff will carry away paint. dry sanding only seems to work for striping with very very corse grit
I think I used somthing like 20grit the paper looked like it had rocks glued to it.
but I ran it on a angle grinder so it it runing very fast. everything else is done wet.
I do level with a long air driven sander and I have to change the paper very very often.
I get the 100packs I I think that is 100 or 60 grit this the the best tool it is like 16inches long and 2 inches wide. sanding with this gives a nice flat job. where everything else starts to get waves.
when you could get the good primer it would not clog. and I would sand in one hand and prime in the other. the stuff was dry as soon as it hit. and would fill most small dings.
I always used a bucket of water and a sponge, I would dip the sponge in the bucket and hold it over the block as I sanded. You need to have a film of water under the sanding block to make it glide, not stick. You must keep rinsing the paint particles away so they don't bond to each other and create "nibs" on the paper. When the paper starts to get "nibs" on it, it will scratch the paint. I used a paint stirrer to slap the paper to clean it.
as all others have suggested, you need to WET SAND when sanding down topcoat paint with anything coarser than, say 180 or so. primers can usually be sanded dry to much finer grits.
when dry sanding, once the paper starts to clog, additional clogging is accelerated - the paint likes to stick to itself.
i always use a bucket to hold the water. a little dish soap in the bucket water can also help if you still have clogging issues while wet sanding. but really, if the paint easily clogs on the paper while wet sanding, it is not cured properly.