MDPE pipe?

The bore would probably be too small for it to drain away at the same rate it could fill unless you had sufficient head, but I haven't done calculations for that sort of stuff in over 40 years.

 

Hi,

If you use a too small bore you could get overflowing around your diverter ?

The Blue pipes are available in larger diameters, if you find that colour acceptable above ground ?

Think we would use the standard black or white 32 or 40mm waste pipes, cheap enough though you may need to use the solvent weld types as the push fit might leak where the water is retained in the pipe under the lawn.

 

If intending to order online for delivery, I think some places don't deliver solvent weld cement and make you go instore to get it (had this problem recently).