I have mine at about 50%. Mine are still in their baby tank though with just the paper towels and some leaf litter. I mist only 1/2 of their tank lightly and provide the water dish. A great person to ask is UncleChester. My previous adult toad preferred it very dry with just a water bowl. The part I'd mist he usually stay out of. He did love to soak though.

The average house room humidity is generally about 50% in the summer and a bit less in the winter due to furnace heat.

Im not sure how you could dry it up. It's so pretty I think I'd keep the tank for a nice tree frog and make a standard terrestrial tank for the toads. It'd be quick and easy. They just need substrate, water bowl, a hide and some leaf litter. Maybe a couple plants to feel at home. Mine had a couple large rocks he used to like to sit on, I think bc they were nice and cool. Honestly, his favorite place to sit was in the food bowl, lol .