Gasketed pipe direction of flow

Dumb question:
When laying SDR gasketed pipe should the water flow from bell end to spigot end or vice versa or does it not even matter?

Yes, Bell end to Spigot end. Less turbulence/obstruction.

pipe

I guess part of the answer would be if that would be a factor with fittings, and since most fittings have bells at both ends it would be impossible to NOT put one the opposite way, although convention calls for the pipe's spigot to be downstream in sewer systems.