Oil bath hub ???

[Hook'em-AND-Cook'em]

My triton boat trailer has the oil bath hubs. If they are like the bearing buddies (grease ones), they put about 3 psi of pressure on the grease/oil to prevent water from getting in the hub. I had the grease type on my old boat and this is done by spring pressure. But what about the oil type? I changed the oil in them, but the site window is flush with the hub now, so there is no pressure exerted on the oil. You can take a pair of needle nose and pull the window out some, but as soon as you let go they are sucked back in. Is there a special way to fill these so that the window stick out and pressure is applied to the oil???