Just a thought, but, there's a chance he's coming to take pictures of the place so he can list it and start looking for new renters. If you have something that looks off or out of place, like a giant stack of boxes, depending on where it is, he may ask you to move them for a cleaner picture. Be prepared with an excuse why you refuse to move those.

Are you friendly with any neighbors? Maybe you can drain half of the tank (same as when you do your water changes, hopefully) and move the tank to your neighbors house, porch, patio, etc on the day he comes. Get those moving furniture straps and you can easily move the tank with a buddy while someone else moves the stand. If you aren't friendly with anyone, just place it outside somewhere out of the way on the day he comes. If the landlord sees it, say it's the neighbors selling it on marketplace or something.

I think best bet is to move it, not hide it. If you do want to hide it, move it somewhere it won't affect a picture before you hide it. Worse case, he'll see it and charge you a fee for breaking the contract. Good luck!