Just got my 1st set of sounding rods and would like some how to advice. How deep can u go.... I've cleaned and lubed the rods so far can insert up to an 8mm about 4 inches into my cock. There I meet resistance even with the smallest rod. How deep can u go....should I try to go past that point. I've watched videos and looks like all go past that point pretty far. How do u go further?