Clearly I had no idea how to grease trailer wheel bearings that have zerk fittings.

[CGMKCM]

Another reference.

 

[mcmxi]

Another reference.

Thanks. Here's the relevant part from the article you linked to.

E-Z Lube® Lubrication

First, you will need to remove the rubber plug from the end of the grease cap. Then place a standard manual grease gun onto the grease fitting located at the end of the spindle. Do not use pneumatic powered grease guns as these can inject grease too fast and force grease past the seal, or in rare cases dislodge the seal. You will want to make sure the grease gun nozzle is fully engaged on the fitting. While you rotate the hub, pump the grease slowly into the fitting. The old, displaced grease will begin to flow back out the cap around the grease gun nozzle. When the new clean grease begins to come out, remove the grease gun, wipe off any excess, and replace the rubber plug in the cap.

Pro-tip: The E-Z Lube feature is designed to allow immersion in water. Axles not equipped with E-Z Lube are not designed for immersion and the bearing should be repacked after each immersion. If hubs are removed from an axle with the E-Z Lube feature, it is imperative that the seals be replaced BEFORE bearing lubrication. Otherwise, the chance of grease getting on brake linings is greatly increased.

 

[mcmxi]

I picked up the boat from storage today and decided to grease the Dexter EZ Lube wheel bearings before starting out on the 70 mile trip home. I took one of my floorjacks with me and a couple of 4"x4" posts that I cut down to span the axles, so that I could lift the entire side an inch off the ground. It really couldn't be simpler to grease these things. Just spin the wheel while pumping grease in until you get clean grease coming out the front.

Yes, the instructions from Dexter say not to use a pneumatic grease gun, but say nothing about a battery powered grease gun. The flow rate is relatively slow with the DeWalt so I can't see it being a problem with seals.

I started with the front right for no good reason and it had chocolate grease in it. I should have taken a photo but figured that they'd all be like that. I got the impression that none of them had been greased since leaving the factory in 2017, but only the front right had taken on water. At first I thought that it was perhaps a brown wheel bearing grease, but I soon realized that it was due to the water.

Here's the front right bearing after I had pumped out the worst of the chocolate grease. I'm going to revisit this bearing in a few weeks and pump more grease into it to clean out any water contaminated grease.

And this is how the other three bearings looked prior to my pumping fresh grease into them.

Ready to head home with greased wheel bearings.