I only clean when needed and as needed, not
as a preventative treatment...Just doing the physical check exam to see if he needs to me is invasive and can be irritating. Does Rusty drop down so you can just do a visual check or must you do a hands-on investigation?
My vet has told me to not "pick" clean but if it is loose remove it, otherwise leave it alone
...some debris is expected but gross amounts of gunk need to go.
If you pick off and pull you just made him sore...not good.
On my geldings when their inside upper leg gets icky marks...time for a gloved meeting to take place.
I use as mild as possible a cleaner, often using the commercial preparation sheath cleaners as they are ph balanced and not abrasive.
Otherwise a very gentle soap, some warm water to clean and large amounts of clean, clear water for rinsing.
Remember you must rinse thoroughly and carefully all residue or you can create sensitivity and sores and a unwilling accomplice next time.
Once you are finished there is nothing left except wet skin so no "attractant" should be around that can create a homing environment to get stuck on or in.
And no, if you are asking do I use something like Vaseline the answer is no.
I have used KY Jelly in the past when doing the exam part as slick is easier on them but a pest for me..and a light use of mineral oil to rid of built up smegma that is evidenced on their upper thigh....
Be careful though as you don't want to upset the beneficial bacteria of that area or you will be looking at some nasty vet bills trying to fix a serious complication made.
Don't forget the exam gloves or wear "the scent" as cologne for a while no scrubbing seems to make quite go away from under the nail-bed.