Water wash out..
Now this grease term I think is from what I have gathered focused on ,
Much like drop points, I mean do your really need a 900* rated grease for a wheel bearing??
Water wash out, pertains to where a grease is directly exposed to water,.,
IE a water pump bearing,
Now if your marine grade grease is going in a boat trailer wheel bearing,
Sealing, good quality seals, properly installed, keep the water out, #1 most critical,
aside from that amount of grease inside wheel hub, they say to much grease is no good, but the more something is filled up the less something can get in,
No two things can occupy the same space, so a happy medium of amount of grease, well sealed, are things to consider as well as what the lube is called