I realized a long time ago that PIPE ends still absorb particles randomly and then eject it at a random time. I know the particles don't flow back to the start but it is kinda impractical when, say, WATR keeps on being attached to the end of the PIPE because the PIPE reabsorbs it and all those stuff... So if possible:

PPEN - Pipe End

       - an accessory element attached to the ends of PIPEs so PIPE ends would not absorb any particles

          anymore.

       - can be configured (through CTYPE) to only let through certain elements

       - (optional feature, include if you want) absorbs particles when powered (one particle per pixel),

         releases when disconnected from power. This makes it pretty much like inverted STOR

or:

It will auto-generate at the end of the PIPE. This way, no more new elements to be programmed. It will just be like the RGB colors inside the PIPE, only it would be dark gray.