37 gallon with corner over flow. It can also be used without the over flow however included will be stack overflow threaded pipe piece. These threaded pipe pieces can be purchased at Menards and can transition to hose to sump if desired. I used these with sponge filters and used overflow just for easy water changes but could go to sump and used with return pump. Second picture shows overflow stack pipe that will be included. EDIT 1/23/24 auction will be for two 37 gallon tanks with over flow. Second tank can also be used with or without the overflow. These are three foot by one foot tanks.