I guess you have a separate cistern and pan, connected by a plastic flushpipe, Flobbers? It's just a simple plastic pipe with an open end fitted into a plastic or rubber connector.
I'm afraid I can't think where the drilled holes may be.
A common fault is that the pipe is too long (on the horizontal bit), and has been pushed too far into the WC pan. This can restrict flow greatly, since the pipe-end touches the pan body and closes the outlet.



