I got on to Jet Lube v2, I think it is called. Expensive but never hardens - so no waste & it does gas, potable water etc.
Boss White is actually a brilliant sealant paste & nothing works better I reckon that it for any hot joints in a heating system as it will ooze into the joint & harden. I actually have sealed joints like on a coil connection at a cylinder by insulating tape stretched over boss white. Not for potable sadly & hardens in the tub unfortunately, but very cheap.