You cannot successfully winterize plumbing "P" traps with air, nor can you winterize a clothes washer with air.
If you replace the "P" traps with HepvO drain valves you eliminate the need to winterize them, but you still need to add RV antifreeze to the holding tanks as previously noted.
Next time you "winterize" with only air pressure, continue winterizing with RV anti-freeze, catch what comes out of the faucets until solid pink antifreeze shows. Measure how much water you catch.
2000 Winnebago Ultimate Freedom USQ40JD,
ISC 8.3 Cummins 350, Spartan MM Chassis. USA IN 1SG 11B5MX,Infantry retired;Good Sam Life member,FMCA." My fellow Americans, ask not what your country can do for you, ask what you can do for your country. John F. Kennedy