Please help!!! Day 18 humidity

Hey everyone, I have been reading byc since I've had chickens, which has been about a year. A lot of helpful info but finally started an account bc I can't find what I need this time. I'm probably just missing something. Anyway, I am hatching 30 eggs in an incubator, it has an automatic turner and is one of those styrofoam ones. It can hold 42 eggs. Yesterday was day 18 and I took out the turner and filled up some of the water tunnels at the bottom with a little bit of water and I put in a small damp rag (ok really it was a small old sock) for the humidity. This morning I wake up and he humidity was down, although when I went to bed it was where it needs to be. I went wth the dry incubating method for the first 18 days and I left the two red plugs out. I still left them out yesterday bc I read they need the air. How am I to keep the humidity up without filling up the basins and getting the humidity too high? I am borrowing the incubator from a friend and she had really low hatch rate bc I think her humidity was too high and she drowned them. Any advice? Oh and I out the plastic cabinet liner and then some paper towels down under the eggs, so in order to fill the bottom basin up, I would have to remove the eggs Sorry for the rambling but trying to give as much info as I can. Any hep or advice is greatly appreciated!

 

Thanks for the reply! I snuck a damp sponge in there and put it under one of the vent holes. Maybe I can use a straw to wet it if necessary. So many different ways to do it but also easy to mess things up, I'll let you know how it goes!