I posted this in the cooling part of the forum three days ago with zero response, so trying again here.
 
Hi all. I'm going to be leaving home for almost a year (deployment). This means I'll need to shut my machine off for that whole time.

It's a water-cooled i7 6900 with a water-cooled EVGA 1080ti.

I've never had to shut off a water-cooled machine for an extended time, and I'm wondering what I should do to it before I leave so that everything will be fine upon my return.

So far I'm thinking that when it's time to shut it down I should drain all the coolant, the flush it with distilled water to clear out any of the green coolant formula that I'm using so it doesn't dry out and leave a dried film on any of the cooling surfaces while I'm gone. I'm not sure if there's a good way to ensure that everything dries out thoroughly before I go. Maybe leave some tubes unconnected but capped with some cloth or something that will keep dust out but let humid air slowly evaporate in my very dry office?

Has anyone got any suggestions for how to do this so the machine can just be refilled with new coolant mixture when I return and be turned back on and used?

Also, I'm thinking that I maybe should just sell the 1080ti before I go, considering there's a high likelihood a new generation of NVidia cards will be out when I get back in the middle of 2019, and because the current pricing fiasco of these high-end cards means the 1080ti still has a lot of value. It's got an EK water block on it and has been running mostly unoverclocked ever since I put it in (the games I've played the most maxed out my 4k monitor refresh rate with no need of any overclocking). Would you guys think that's a good idea?

I leave my computer off for a month at a time for similar reasons. Personally, I would ensure quality coolant was used which had biologic growth inhibitors and corrosion inhibitors (and a coolant you have used for quite a while and trust), fill everything to the very top (no air in the system), and keep it out of direct sunlight. That's what I do. I would be more worried about dry rotted gaskets/seals, additive/die/mineral film ("gunk"), bacterial growth, pools of trapped liquid exposed to lots of air/bacteria, and oxidation which may occur if the system is left empty.
Remember, if you leave your car in storage, a full fuel tank lasts much longer than an empty fuel tank.

Thanks for the comments guys! I wasn't thinking of selling the mobo/cpu/ram but maybe I should. I don't know what the market is for used i7 6900s but ever since the Ryzens came out that are only just slightly slower I can't imagine it would be all that high. I do have a laptop (bought it to take on my previous deployment in 2014) that I'll be taking with me, so I could just keep using that when I get back while I buy up parts to rebuild my machine. I'm not experienced with selling computer hardware since I typically just use it for several years and then do a full rebuild/upgrade with much better parts. I was expecting this i7 6900 to serve me for a good 4 or 5 years.

So I guess I will drain and flush the machine, especially if I sell the 1080ti. I'm less inclined I guess to sell off the cpu because it's still a killer cpu, and will be for some time. The 1080ti was able to max out my 4K monitor at 60hz in any game I tried, including (barely) Witcher 3, so it's not like I really have to have the latest and greatest when I return, though the hardware hound in me disagrees, whispering "actually yes you do" in my mind.

I got the i7 6900 for half price from a friend, and lucked out on the 1080ti, having bought a 1080 SC originally, then did the upgrade they offered to the 1080 SC2 when they offered it. That reset the step-up timer, right before the 1080ti came out, so I stepped up to that, something like a year or more after buying the 1080 originally! Only EVGA.

The deployment will be my second, and probably the last major thing I do in the military. I'll be eligible to retire a year after I get back. Rebuilding my machine, with some upgrades, would be a nice way to celebrate coming back home. Btw, my avatar photo is my current machine, and yes, you could say the cooling loop is custom. It's more like a bastard loop. I'm using the Swiftech 2x120 radiator/pump combo (has a much more capable pump than the typical AIO pumps) as the pump and secondary radiator, and spliced in a massive 2x180mm radiator with those four goofy fans in push/pull mode. The radiator is so large there was no way to conveniently get it inside the case, so I fabricated a wooden mounting bracket for it and clamped it with woodworking clamps to the side of the case. It's ugly as sin but works extremely well. If I rebuild the machine when I get back I may retire the Swiftech and replace it with a conventional stand-alone water pump, but it's worked well, so I might just keep it in there as long as it still works.

for that long if you keep everything i would drain and flush it then pull everything apart and dry real good, you can use a bit of oring grease to keep the seal from drying out, that pretty much what the manufactures use, personally though unless you have some emotional attachment to the parts i would just sell them while prices are still higher and bank the money til you get back, todays top parts will drop some by then so you can build a better system next year, as for setting prices i would look at some forum market places like here and maybe heatware and few others to see what your parts are going for and then post them up here in the marketplace.