RE: ys170dz Fuel tank
I have the same setup with my YS170. Two fuel dots, one in the overflow line & one in the feed line. At the end of the overflow fit your oneway valve. It should be installed so it lets air into the tank. I check this by fitting a unused bit of tubing to one end of the oneway valve, and sucking air in my mouth. If it allows air in, then thats the end to the overflow tank pipe. Only two pipes needed to the tank, overflow & feed. The tank I use is a Tetra 20 oz.
There is no additional pressure needed for the 170, It's a pumped engine.
When I fill the tank, I clamp the silicone pipe inbetween the pump and fuel dot with a long nosed pair of surgical scissors clamp. This will prevent fuel being forced back into the engine when you fill the tank, I also clamp the pipe through the cowl as soon as I land. Theres a commercial items avaliable you can buy that allow you to clamp the fuel line from outside the cowl. I'm sure Central Hobbies have them.
Mike