You can use isopropal alcohol but just don't ingest any. Make sure you shake the atty out well afterwords and dry it well. Then be sure to prime the atty w/juice before you use it, especially where you see the white wick under the atty bridge and then let it sit upright for a few minutes so the juice will hopefully get to the coil and prime it.
Blue foam - M401 carts are small enough that you can but plugs from the larger cheap precut pieces for 510 at strictlyejuice.com. if you want to buy the bulk, it costs 10x as much and is Marineland Rite-Size U Foam Sleeve in the aquarium dept of Petsmart. I think it works as wekk as brand new white stuffing and stays nice a lot longer.
Search Youtube for M401 Blue Foam
The guy the video is using a similar gray foam that comes in a bigger block. The blue foam is thinner and its thickness is just right for M401 carts. He is cutting a pretty extreme plug. I recommend instead you cut the plug about 3/4 the inner length of the juice cup and a tiny bit wider to discourage it from slipping down in the juice cup. Like cut a straight piece out of the foam the same width as the thickness of the foam and only round the long way corners of slightly. Not too wide or that will press the foam holes closed and it won't wick well. Taper the inner end of the plug a bit. A small smooth unbent paper clip is helpful for positioning blue foam. before cutting, many recommend rinsing the blue foam then pat totally dry with a paper towel. Shouldn't really needed since it is safe for fish but good idea.
On a full fill, remove the foam, fill the juice cup 1/2 way with juice, insert the tapered end of the blue foam, and then push the blue foam down into the juice to wet it. Then reposition the top edge of the blue foam at the top edge of the juice cup, and top off with 1-3 drops, just whatever it needs to look damp on top. Don't overfill. Then just like with the white stuffing, top off whenever it needs it, and when topping off doesn't help much then it is probably quite dry so do another full fill.