this is from MR. heater. if you get the 10′ hose you will not need a filter.
In most propane appliance situations, there is a regulator located at the tank, followed by a supply line. In that situation, what passes through the hose after the regulator is low pressure gas. Low pressure gas is harmless to rubber. The buddy system has the regulator located at the heater. In this setup you cannot have a regulator at the propane tank due to over-regulating the gas supply. This makes the gas that passes through the hose to get to the buddy system high pressure. High pressure gas squeezes rubber as it passes through it, and can occasionally pull some of the oils and plasticizers from the hose during these periods of high pressure. Those contaminates will travel with the flow of propane and land somewhere inside the heater, slowly building up over time and causing gas flow problems once the buildup becomes large enough. The 10′ buddy hose does not contain any plasticizers or oily contaminates that will leach out of the hose during high pressure propane flow. That is why that hose does not need a filter. All of the other hoses for the buddy system will need a filter because they will contain oils and plasticizers.