If it were me I would fill it up, put a cup of dichlor, let the pumps run (unheated) for about a total of 2 hours while the whole thing sits for about 24 hours. For added measure, I would run something like swirl away in it, fill, drain and fill again ... you have now disinfected and cleaned the entire inside of your spa.
I did the disinfecting thing when I first got my tub just in case there was some nasties around.
Just my $0.02!