if it's properly sealed and the wax / sealant is still there and working ie not left for months and worn out, it should wash off quite easily. all dependant on what wax or sealant you are using really? When it won't just wash off with basic shampoo you know your wax has worn off.
What do you use
I've only just started out really, so at the moment only by hand, recently Clayed / SRP/ EGP / Megs #16 wax, about a month ago.
Been washed a few times since, and do top up the wax every few washes
It does come off with shampoo, Its just if it doesn't come off when blasted with the hose, I'm always worried about using the mitt, coz I'm worried about getting the mitt dirty and scrubbing dirt around, on the lower sides, coz they're really dirty. I do leave them till last though, but still, don't want to ruin the mitt for the next wash.
I guess a pressure washer would be better at getting it off, rather than a finger over the hose lol. Lucky just bought a cheap Nilfisk