[BeerSmith]

A friend recently gave me a pressurized water tank of some sort that has similar anatomy to a corny keg. I've got it fitted for gas in and liquid out, but there's an extra threaded hole that's currently occupied by a pressure release cap (at least that's what I think it is, I don't know what it's actually called). Should mention that it has a proper pressure relief valve so that's not an issue.
So my plan is to take off the cap and mount a gas in with a carbonation stone there. Is was working on a system that would allow me to pull it out after carbonating, but that went out the door when I realized the stone itself won't fit through the hole. So plan B is to semi-permanently (it'll be on threads so I can remove it for cleaning) mount it and just leave it in the keg for the life of the batch.
So my question is, would leaving a stone in the beer for several weeks either gum up the stone, or possibly cause it to break down in the beer?

[hopfenundmalz]

If it is stainless steel, it will be fine.

[a10t2]

...To elaborate, the stainless won't be harmed, but the stone will definitely get clogged over time. You'll want to rig up a way to circulate your cleaning and sanitizing solutions through the stone in both directions when you break it down.

[brewinhard]

A long boil of the stone may help to degunk some of the crap from fermentation.

[hopfenundmalz]

A long boil of the stone may help to degunk some of the crap from fermentation.

If it can be removed, dumping boiling water in will be the next best thing.

[Robert]

A friend recently gave me a pressurized water tank of some sort that has similar anatomy to a corny keg. I've got it fitted for gas in and liquid out, but there's an extra threaded hole that's currently occupied by a pressure release cap (at least that's what I think it is, I don't know what it's actually called). Should mention that it has a proper pressure relief valve so that's not an issue.
So my plan is to take off the cap and mount a gas in with a carbonation stone there. Is was working on a system that would allow me to pull it out after carbonating, but that went out the door when I realized the stone itself won't fit through the hole. So plan B is to semi-permanently (it'll be on threads so I can remove it for cleaning) mount it and just leave it in the keg for the life of the batch.
So my question is, would leaving a stone in the beer for several weeks either gum up the stone, or possibly cause it to break down in the beer?

I've dreamed of such a rig for ages, but don't have a friend handing out gear like that.  What the heck was the thing intended to be?  Was it threaded such that you were able to just put standard corny poppet valves on it? So many questions, head spinning, visions of scrap yards heaped with these unicorns...

[Philbrew]

In between boil cleaning, a short soak in Everclear will sterilize.