Toilet supply tubes work perfectly and cost $3 at Lowes or Home Depot... I used it for a trim line in my 750 and just put one in the SJ in case I decide to install trim.
You want 3/8" o.d.
I'd do this in stainless:
8989K482
(Same as 8989K481)Type 304 Stainless Steel Welded Tubing 3/8" OD, .319" ID, .028" Wall, 3' LengthIn stock at $6.39 Each
$6.39 for 36" of it, even if it doesn't work it's not a huge waste. www.mcmaster.com Oh, you'll probably have it tomorrow if you order it today.
except those lines arent stainless. they are plated steel. i looked into those when i was drilling a dual cooling line through my hull.
i dont think it would last a season in salt water for me.