Tube platform is packed everywhere to begin with (4)
I believe the answer is:
pipe
'tube' is the definition.
(pipes are tubular)
'platform is packed everywhere to begin with' is the wordplay.
'to begin with' suggests taking the first letters.
The first letters of 'platform is packed everywhere' is 'PIPE'.
(Other definitions for pipe that I've seen before include "Tube carrying liquid or gas" , "Meerschaum" , "Part of an organ; tube" , "Something in the organ loft" , "Fluid or gas transporter" .)