Washing RO-DI reservoir

[asylumdown]

I don't think you're going to have a problem. The amount of dissolved solids left over in the bottom of your tub from washing it out with tap water is going to be practically non-existent when you fill the tub back up with R/O water. There are also lots of people who keep reef tanks in just tap water, so the minuscule contamination you're going to get will hardly make a difference.