I have just recently changed all the brake pads on my Street triple - regrading the use of grease :
First of all I used an aerosol of disc brake cleaner to clean all parts of the Brake Caliper when removed from the bike and discarded the old pads .
I smeared the outer walls of the brake pistons with Red Grease & pushed them back into their caliper then , I smeared the back of the Brake pads with Copper slip Grease as well as the Pad retaining Pins .