I kept and bred both YT and Easterns in setups similar to that, smaller but hide accessed through a hole in the bottom.

They did, mostly, crap in the bottom. Not always though. I kept False Water Cobras the same way. If I recall, and it's been a while, they just went wherever whenever.

Are you breeding your YTs yet? I bred mine in 92 and 93 then entered into a partnership that went south and haven't had any since. They were one of my favorites of all the snakes I've ever kept. I think my male was over 9 feet.