Leaking Vents

Yosef Guttman

Looking for some Ideas
I live in a hundred year old house which was designed with City Steam as the source of Heat. Scranton turned district heat off some time ago (my house is well into its second boiler.)
Problem is currently I have the last vent on my system is leaking water (Previously the f&T trap below it would leak water out of its vent before I fixed it(covered the vent with electrical tape no more leak)

What I am thinking is that originally the steam came in the back of the house and exited as condensate the front of the house(which means all the returns are piped sloping to the front of the house)( I know the return line goes from floor level up to about 24" high at the back of the house before it goes under the floor of the basement and comes back up near the boiler) With the boiler (instead of central steam) the boiler is in the back of the house but the condensate has to get back to the boiler going up hill. Is it possible(likely) that the return line has accumulated so much rust and silt that the return water cannot make the trip back to the boiler and therefore is leaking out the first possible exit(the steam vent on the first floor) i was going to try to hook up a hose at the front of the house at the condensates lowest spot and run it back to the boiler (There is a hose bib on the return line for some reason) and see if that helps
Currently I am adding water every 2-3 days to keep the boiler running(I know that is baaad but the wife and kids want heat)
Just looking for some thoughts on it.
Yosef