There are two things. most any lubricant will work Engine oil Silicone Dri-Slide (Very messy but very good) Even WD-40 if you do not mind spraying it EVERY time (not a good lube choice, after all it is a cleaner)
And yes, Dish or hand soap will work too (Better than WD-40 in fact).
Just do not change lubricants once you make a choice.
Usually if it is not sliding easily it is because the hitch is not dead center on the trailer,, I have found many times when a bit of pressure one way or the other on either the trailer or tower allowed it to latch easily.
Of course the "Bit of pressure" works a whole lot better on a 2000 pound trailer than on a 20,000 pounder