Plugging holes in planting pots to bring in house

Last year I had a terrible fungus gnat problem. My use of spagham moss to plug holes kept too much moisture in pots.

Over the years I have used so many different materials, and none seem to work. Either stays too moist, or I loose soil. Using good soil-less mix, don't water unless necessary; wash the plant roots before re-planting.

Looking for ideas beyond broken pot pieces, styrofoam, peanut packing materials. TELL ME IF YOU'VE USED SOMETHING THAT WORKS.