Several times I have circumstances when I would like to put an additive into the tank when the tank was already filled [by wife for instance or not available at time of fill up]. Most additive directions say add product then fill tank. I assume this is because they want the fuel to wash additive from inlet into the tank or allow fuel flow to help distribute additive. Is there any problem with adding additive to a full tank then using a little fuel from the lawnmower can to wash additive down then moving vehicle to mix it?