G'day Dimitri,
The hose from the Leg to the Pump is carrying cold water, and therefore there is no requirement for a High Temperature, or High Pressure hose for that matter. In fact, either single, or double reinforced rubber hosing is sufficient.
Plus, if your engine cooling is an open Raw Water system, there isn't that much pressure involved. Even with a Closed System, the pressure involved will only be the limit of the Pressure Cap, which shouldn't be above 15 Lbs.
But, using Plastic fittings in a cooling system isn't advisable because if it fractures there is the possibility, and probability that you won't notice it till your feet start getting wet, or the engine siezes if the Temperature Gauge isn't being observed.
Some thinks there is no compromise on, and plastic fittings where water from the outside is concerned, I always make it a requirement that Brass, or Stainless Steel is used, and if it is a Skin Fitting, then a tap attached before the hose is attached.
Bruce.