Kvass (wheat/bread soda) from used grain

I'm new to brewing, and my wife doesn't want me to spend lots of money making beer. So I started with all grain beers. After I sparge the grain and have my wort and yeast in a fermenter I go back and make Kvass. It's a bread based soda. I re-steep the grain as if I am making another beer, but I don't sparge. I add a cup to two cups of brown sugar, and a teaspoon of bread yeast once the wort is cool enough. I let this sit out for 3-6 hours so the yeast have a chance, then I bottle it in old two liter bottles. I then put the bottles in the fridge. If the bottles seem to be too tense I let out some gas. I've only made kvass twice, and the first time it was a gusher, so I went from a tablespoon to a teaspoon of bread yeast. It does have a yeasty flavor and this also is why I decreased the quantity of yeast.
After 3 days I start drinking it. I've seen online that it will stay up to three weeks in the fridge before turning.
It's sweet, carbonated, and it will let you know the future color of your beer. It will also give you an idea of what your beer might taste like.

Awesome, I am enjoying a glass of a traditional recipe bread kvass right now and got to wondering if I could make it with spent grain. I'm definitely going to try it now. Thanks for sharing your experience.

What temp water do you use and how long do you let it soak in the grains?

I treated it like a beer I was brewing. I probably would just boil it next time without steeping it.