https://www.youtube.com/watch?v=XT0RKDGgDm8
On the other hand, another youTube video proposes to show the grease system will tend to blow out the rear main seal and contaminate the brakes. You can start watching at this point:
E-Z Lube Hubs Exposed
https://youtu.be/1B_E7khBenQ?t=134
Most of the comments about this presentation point out that the demonstration is not particularly valid because the whole system was not in place. When all components are in place, rear seal, inner bearing, outer bearing, front seal, retainer washer, nut, locking mechanism, the grease will tend to flow as intended, as long as the rear seal is in place and the exiting grease has not hardened and won't easily be pushed out.
Useful comments cite the requirements for successful use of the E-Z-Lube system:
- the wheel MUST be rotated continually as the new grease is pumped in;
- only perform greasing on a warm day;
- be sure the grease temperature is warm; and
- pump in the new grease slowly
Leaving the grease, the grease gun, and the wheels sitting in the sun for several hours is recommend before re-greasing.
A very cogent comment mentions that for each pump-in of new grease, you should see a corresponding appearance old grease escaping. If you do not see that occurring, then the new grease may just be blowing past the rear grease seal.
Another comment--perhaps the best--cites the machined exit hole for the grease as having a sharp edge. The sharp edge tends to cut into the grease seal, reducing its effectiveness. That user recommends de-burring the the machined hole edges. If you do this, be sure to remove any metal shavings or particles created in the process.
A further caution is to AVOID using a powered grease gun; always pump in the new grease using a hand operated grease gun.
The most reliable method for boat trailer wheel bearing maintenance may be a periodic complete disassembly of the the bearings and seal, replacement of the grease seals, cleaning off of old grease, and re-greasing with new grease, including preloading the bearings with grease (which can be done with a handy plastic cone accessory). That is much more work than using the E-Z-Lube method, and might not be possible for everyone do accomplish.