Where I work we service a lot of trailers like Yosemite’s with surge (hydraulic as opposed to electric) brakes. On these trailers the tongue telescopes into a channel in the frame of the trailer; then it pushes a pushrod that pushes the piston in a single piston master cylinder. All this happens, of course, when the towing vehicle brakes, effectively pushing the tongue into the frame’s channel. Theoretically, you can use a long 6 by 6 to lever the tongue back into the channel & actuate the master cylinder. You join the 2 safety chains together & lay them forward on the floor. The end of the 6 by 6 goes against where the 2 chains connect. Then you stand on the front of the trailer & pull the 6 by 6 back against the tongue, engaging the master cylinder. I have NEVER been able to make the tongue move this way, even with help from 2 other people!
I think Yosemite is right, but can’t make out exactly what he is saying. There is a lever about 3" long sticking up out of the front of the trailer frame, just behind the tongue. It pivots below, where you can’t see it. One end of the “breakaway” cable is attached to the top of the lever, the other end to the towing vehicle. If & when the towing vehicle breaks away from the trailer at speed, the cable yanks the top of the lever forward; the lever pivots & the bottom of the lever goes backward, engaging the master cylinder. Notches on the lever then engage a plate bolted to the top of the trailer frame so the lever can’t release. Now the brakes stay engaged. So, to bleed the brakes, you unbolt the plate & remove it. Put a long vice grips on the lever. Pull lever back & forth to bleed. Re-install plate.
Hey Yosemite! Don’t forget–these drum brakes are not self adjusting. The other week I fixed a leaking brake tube on a trailer like yours. I bled the brakes as per above. No braking action. Boy was I p***ed! Then I adjusted the brakes. That was what it took.