Peanut and Franco's Mud Pit

[bclaytonphoto]

We have two grey tree frogs in a 30 gal tall tank..Peanut the male..and "Mama" Franco the female..
They have two water dishes in the tank..One is a rock like "dish"..the other is a "groovy jacuzzi" that sinks into the substrate..
I've been finding the jacuzzi with most of the water missing..and filled with substrate..
I thought the thing was leaking..The other night I got home late and found Peanut sitting on the edge of it...covered in mud...
It has been very warm here in Central NY recently.( upper 80's to low 90's).I was thinking this was a way for him to cool off?
Has anyone seen this behavior before?
The tank does have a humidity control device..Obviously I'm not running the heater this time of year..

[Mentat]

Your toad might be using wet substrate to cool off . How deep is your substrate layer and is it slightly damp? If shredded coco fiber, it should be damp enough to clump in fist but not drip water out.