odor from radiators

Philip

We have been experiencing an odor in our 1890 farm house with steam radiators. At first, we thought it was coming from the garbage disposal, so we tried several methods to solve that, but the odor continues and now we are noticing it in different rooms besides the kitchen. It smells like
something rotten...almost like a decaying animal...
I read on your site that you suggest using trisodium phosphate to get rid of odors in the radiator system and boiler. Please tell me how to do this. Thanks