there is a plethora of information on this process on the infamous interweb...
i found a guy who shows how i grease bearings by hand
only takes minutes and not worth the expense of buying a packer
http://www.bing.com/videos/search?q=rep ... &FORM=VIRENITRILE GLOVES!!! knot latex
i have gone to waterproof grease, the blue/green stuff, for all 3 of my grease guns, shop, boat trailer & farm implements
it is a step up but not cost prohibitive by any means(the difference wont prevent you eating @ THE GOLDEN ARCH CLUB)
i have also begun(almost finished) changing all my dust caps to the BEARING BUDDY system so i don't have to remove the hubs each time they are due for service
once you have done a thorough service and installed the new caps you will rarely need to pull the hubs for service, just jack the tire off the ground and spin it listening for any gravely grinding like noises
if spinning the tire sounds smooth, just inject grease thru the nipple until the plunger moves outward nearly to the edge of the cap and move on to the next tire/wheel
over greasing using this system tends to force a bit of grease out the back/seal and does not necessarily mean the seal is damaged
i use this method on all my trailers, RV, utility, farm & boat and have one trailer that went over 20 years w/o needing to repace the bearings and it was subjected to fresh & salt water launchings, regularly
if you do go this route on a boat trailer make sure you lube the BUDDIES at the ramp just before launching, in addition to the beginning of longer trips which fills the hub and really helps prevent water intrusion
for your other trailers annual greasing is usually adequate
as for your question about cleaning, there are as many schools of thought as there are trailers...
some say gasoline leaves a film that prevents the grease from contacting the metal bearing surfaces
we know carb &/or brake cleaners will make your babies be born'd nekkid, toofless & bald head'd if you get it on your skin
most professional shops use a parts cleaner vat w/ solvent running out of a tube to rinse the parts, bearings & hubs, thoroughly
Varsol is another solvent that has traditionally been used for bearing cleaning
mineral spirits does work, is less unfriendly to the users and can be had just about anywhere
over the years i've used all of the cleaning methods i mentioned and have not had any known issues with any of them
¿ did i say NITRILE GLOVES ?
work in a well ventilated area
wear safety glasses during the cleaning process
extreme care should be taken when disposing of rags & paper towels
hope this hasn't muddied the issue too much
sw