Block off main drain lines in basement

[mytime]

I have two drain pipes coming up from my basement floor that are capped. My home is about 80 years old and I would like to know if they are tied into the two drain lines that also go into my basement floor and which now do my draining of my fixtures. How would I check these out to see if they are connected to the main sewer line?

[hj]

Without seeing them ourselves, or having more information we cannot tell you.