My house was built in 1938, my tub drain goes into a dump trap. Why do I have 2 exits on the dump trap instead of 1 in and 1 out? Where does the second one go?

my house was built in 1938, my tub drain goes into a dump trap. Why do i have 2 exits on the dump trap instead of 1 in and 1 out? where does the second one go?

These are called "drum traps, and,as a rule, have only a inlet and a outlet,(see image). They are for the most part installed unvented, however, yours sounds like it had a opening for a vent. Regards, Tom

The drain from my tub leads to a dump trap which has been partially clogged since I moved in some 11 years ago. I have tried everything, but nothing works - it still drains slowly and the tub start to fill up when takiging a shower. My problem is I can't get the cover off the dump trap to give it a good cleaning. Does anyone know how to remove the cover of the dump trap. There has to be some plumber tricks, it has been sealed since 1938.
Thank you in advance.
Zarcon50

For those hard to remove covers I take a chisel and hammer and I tap the cover counterclockwise until the cover starts. The cover's made of brass so it's not rusted on to the trap body so once you get it started there should be no problem removing it. Good luck, Tom