Which Stretch series for tight Piriformis

I also run and I decided to cut short yesterday's long run as from the start I felt tight in my glute (probably piriformis) and particularly when running down hill (probably because it was stretched) I felt tautness all the way down the hamstring into the back of the knee.

Just wondering which stretching series would it be good to start to help with this?

Thanks in advance

Andy 

The Middle spilt stretch course would be the one to adress Piriformis.

Thanks @Mats

Middle split is certainly more hip/piriformis; front split is naturally more focused on hamstrings and calves They're both excellent.