How do I unclog a return line on this 2 pipe steam system?

How can you remove the piping after the trap with removing the trap? (Just clarifying)
Remove the ell on the right and run a threaded rod through it. If not blocked there remove the ell on the left and do the same. If not blocked their good luck!

Another way would be to use a drain clog buster sized for a bathroom sink drain by removing the steam trap and attaching a reducing bell and long pipe nipple which would be used to hold the drain blaster in place and slide the drain clog buster in the nipple and use a garden hose to apply water pressure to the clog and flush out the blockage.

I would suggest first dis connect and see if you can blow through it w no restriction if there’s some restriction then I would suggest to disassemble the horizontal return piping from the return to where the vertical drop is ,I ve run into a few where there’s just a blockage of rust at the elbow going from hortizontal to vertical . Last one I ran into I was told they had used a air compress and the line was clear yet refused to heat ,I disassembled the dry return and found it jam packed w rust ,took a pic and sent to building owner ,flushed it out very well snake the vertical piece and reflushed ,fired her up and all was good . This is the best advice other wise you’re wasting your time .i highly suggest not to use a drain cleaning product it will possible clear it but who would add drain cleaner to a steam return not I said the tin man . Drain cleaner is what it says drain cleaner not steam return pipe cleaner it a cheap attempt which will usually garner no rewards and will definitely need to be complete flushed out a steam it would drastically alter the ph of the water in the boiler and possible cause excessive corrosion in any pipe that it is no to completely flushed out of . Just a bit of small advise
Peace and good luck clammy

It is possible to be clogged but far more likely that there is a pitch problem and it is trapping water somewhere(assuming all of the traps on the system really are working properly).

Neither steam mains nor dry returns on two pipe steam systems clog. There's nothing to clog them. Pitch problems…

And maybe a plumber familiar with steam…

" The return line on this radiator is stopped up and prevents radiator from heating. "

Have you actually proven the pipe is plugged up by pouring a fair amount of water into the return with the trap removed ? And the water does not drain. If the water drains fine, you probably have a pitch issue on that return puddling water so the radiator won't vent.

I think you are responding to the original post from 2023. @richarddowling was told his rad supply is clogged. Just disconnect the union on the rad valve, and turn on the heat. If you get steam it's not clogged and you need a new service provider (which is likely what you'll find). If there is not steam then someone probably used some incorrect material somewhere along the way.

@4GenPlumber Yup you are correct. I guess if you want better answers you start your own thread. Using an old thread with different issues may not be helpful.