Cutting ACO drain and end piece

[markyyyyyy]

I need to cut my final piece of ACO he drain, but I also need to install the end cap. Once I cut the end piece, I believe there will be no place to ‘slide the end cap on the grooves’ as per pic

So, how do I install the end cap on a cut piece of ACO hex drain?

Cheers

 

[sparkymarka]

Cut and glue / silicon