Hopkins Carter is a good choice for all your materials. They have a presence on this site.
If you haven't bought the tank yet, Ronco Plastics Ronco Plastics Marine Catalog
is your best source...they make TOP quality rotomolded tanks
for a very reasonable price
and have more than 400 shapes and sizes, over 100 of which are non-rectangular. And they install fittings in the sizes and locations specified by the customer when they make the tank. And they're great people to work with.
And I'd go with Trident 101 sanitation hose... Trident Marine: Sanitation Hose
...it's been on the market for nearly 20 years without a single
permeation failure, something that cannot be said about ANY other hose including SeaLand's highly touted OdorSafe. In fact, I've been aboard at least half a dozen boats on which OdorSafe had failed and have heard of dozens more.
Btw...the v-berth is the best location for the tank for a head
that's forward in the boat.