As I´ve already mentioned, your labpipe has the wrong shape at the top. Have a look at this pic:   my very amateurish drawing should show an enlarged version of the top of the labpipe, showing the shape it should have.      Have a look at the reference pic again and try to somehow emulate that shape. Shouldn´t be too difficult as you don´t have to pull it apart again, just add something at the top.