Sandpaper or DMT for lapping hones

I have been reading for about two years about flattening hones with various materials, sandpaper and DMT diamond stones of various grits seem to be the leaders.
I have come to some conclusions:

#1 I have rarely bought hones that were flat when the sellers claim that they are.
#2 I have never been able to flatten a hone on sandpaper even when using a granite surface plate for a base. It will erase all the grid lines but when I go to a DMT 8c I find that it is not, in fact, flat. When using the DMT first and re-gridding the hone, it will show that it is flat when checking it with the sandpaper and surface plate.
I checked my dmt stone for flatness and it appeared to be flat using a Starrett straight edge and also a dial indicator on a granite surface plate.

Sense my DMT was showing some wear I ordered a new one and now use it to check one DMT against the other on a finished hone, and also to reassure myself that Sandpaper doesn’t work.

I am not saying that you can’t sharpen a razor on a hone that is flattened on sandpaper. I am not sure if it “isn’t good enough to get by” but none the less it’s either flat or it isn’t.

(I also use the Shapton glass lapping plate for my ceramics and the DMT lapping plate for stones that need a lot of work but far it too aggressive for most flattening procedures)

Stingray

I have used my DMT 325 for lapping most everything from shapton 16000's to course Carborundums. I do use fine 3M wet/dry paper "wrapped" around my DMT to do fine lapping on fine grit stones. This is done under slow running water. the paper has always held up.

I do the same as Hirlau

DMT is a better option. I have personally used the Norton lapping stone which also has slots to wash away the slurry, but I've only used it on my Norton 4/8