Deflating through the valve isn't too bad. It's kind of natural.

I remember a friend who had big toys as well and his parents sneaked in his room to poke the big inflatables with a needle a few times. It's a very sneaky move and kind of cowardly as the leaks will be slow and almost impossible to detect. :X

I'm not trying to scare you.... I'm just saying. >'===='>

Wow, that sucks. I know my mother wouldn't ever do that, but if she did she'd quite much regret it. Why did his parents do that anyway <_<

Besides, I like my inflates puffy and shapely, deflation isn't my thing.

Does leaving them inflated stress the seams?

Nah, I don't leave them that tightly inflated either, it'll only stress the seams if you put weight on it or something.

What about sunlight and fading?

He isn't in direct sunlight, and it does take quite a while (speaking: serval months) for an inflatable to fade/stiffen in direct sunlight.
Don't worry, they're not thaaaat hard to maintain x3

*closes your drapes and throws a white sheet over the inflated* ;3