I can't remember for the life of me the name of the product that is the alternative to a Bearing Buddy type system for trailers. Works differently is all I can remember but actually removes the old grease when you pump in new stuff.
Could it be Sure Lube? I know with these the grease flows through a zerk fitting on the cap through the bearings and out the rear of the hub.
Doesn't ring a bell. I just looked however and it might be as I remember the other system's benefit was that it removed the old grease. Which this appears to do. But looks like you have to use their "Transcom" inner seals. Not sure if the system can be fit to existing hubs or if you have to buy hubs. I'm gonna just get the Bearing Buddies. Here's the link for the "Sure Lube" http://www.reliabletool.com/products/slgrease.htm