Well As far as i remember i have seen 90% of the time these desi ac mechanic forget to put this pipe back in
but i alwas remember and remind them to install this properly.
Another point Vchang said above thats what i do, around 2 to 3 mins before i have to stop i turn off my a/c and put the fan blower to maximum so the eveporator/cooling coil gets dry and drains all the water :p.
Also in Pakistan its better to keep fresh air to stop position bcoz we dont have any filters in our cars blower so this also cloggs the cooling coil.
Last week my ac wala take the cooling coil out after 5 months usage and it was just like brand new, even though without any filter so he didnt even bother to clean it just put it back in as it is.