We were in the same boat a couple of years ago looking for a termination cap for our '64
. We eventually found one, after searching for two years, on ebay...they do come up occaisionally. So we didn't modify our outlet however we did look into doing it. You basically cut off the end of the outlet and either epoxy or otherwise bond the new fitting to the existing sewer line. Then the standard fittings can be used...kinda kludge, but it works...we decided to hold out for the original term cap even though everybody told me it couldn't be found! Patience paid off...good luck on your search!