My pump is installed on a sailboat for fresh water. Fresh water tanks are flexible and there is often air passing into water hose. I must unscrew the air vent cap to remove air and prime the pump. I wonder if I can install an automatic air drain, like on radiators at home. I don’t find the characteristics of the air vent cap screw. Could you help me fixing this? I assume many people have this problem with flexible tanks. Thank you