What about removing it in future and going with an "above ground" overflow. That is what I did a several years ago when I had similar problems due to my contractor not putting any collars on my pipe. I told him we would have problems but he wouldn't listen to me.

I have an channel now that is stone lined and above ground that water flows into when the water level reaches a certain height. It funnels into an above ground pvc pipe that has a downward angle and the water dumps into a ditch. The above ground pipe is covered with stone to keep it from moving and for asthetic reasons.

I believe it is foolproof now.

I feel pipes even with collars are just a problem waiting to happen even if it is years later.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.