My September 2017 visit to GP Gliders

I fly NM with water regularly, both in the wings and the tail. I generally fly dry in the early spring when temperatures are still sub freezing at 17,000+ and start filling up during the summer. No problems so far, but if I do decide to use water in the tail tank when it's really cold, I can always add some propylene glycol antifreeze. Several of our more manic pilots do that and it seems to work well.

On Wednesday, August 19, 2020 at 8:03:49 PM UTC-7, wrote:
I fly NM with water regularly, both in the wings and the tail. I generally fly dry in the early spring when temperatures are still sub freezing at 17,000+ and start filling up during the summer. No problems so far, but if I do decide to use water in the tail tank when it's really cold, I can always add some propylene glycol antifreeze. Several of our more manic pilots do that and it seems to work well.
Not telling you what to do but in the Truckee/Minden area it is routine to fill the tanks and fly all day at sub freezing temps - probably 4 - 5 hours below freezing. We did have one case of the tail tank dump valve on a DuoDiscus leaking, which dribbled water onto the rudder hinge and controls, which froze the rudder in position. Pilot flew carefully home on a 200 mile final glide, descending through warmer temps and it melted enough to break loose.