If you have only one valve system then you have a 'check valve' in hot out
(valve handle parallel with cold water line---allows cold water to go into water heater / valve handle perpendicular to cold water line----bypasses water heater *connects cold line to hot line*)
So either valve is not turning and allowing anti-freeze in thru cold inlet
OR
Check valve in hot out is leaking allowing anti-freeze to back flow into water heater
I prefer a 3 valve system (Cold/Bypass/Hot) and NO check valve
The RV anti-freeze is not toxic so a good strong rinse/flush come spring
Might have to do it again after 1st heating cycle
Is it time for your medication or mine?
2007 DODGE 3500 QC SRW 5.9L CTD In-Bed 'quiet gen'
2007 HitchHiker II 32.5 UKTG 2000W Xantex Inverter
US NAVY------USS Decatur DDG31