Sand would be easier than clay. That way you arent trying to scrape it out; you can simply use a relatively high pressure water stream to flush all the sand out.
Species being kept:
Solenopsis "plebeius", Camponotus vicinus, Camponotus maritimus, Formica cf. subaenescens, Formica cf. aerata, Lasius cf. americanus, Lasius aphidicola, Lasius brevicornis, Lasius nr claviger, Nylanderia vividula, Temnothorax rudis and a Hypoponera sp.
Hoping to find this year:
Myrmecocystus, Liometopum occidentale, Camponotus essigi, Camponotus fragilis, Manica bradleyi, Formica perpilosa, Pheidole hyatti, and a Parasitic Formica sp.
People are stupid. It explains a lot...