1998 Chevy Tahoe water leak

We have to put water in about every week about a gallon it doesnt overheat and it isnt the water pump u can see it coming down the engine block. Could this be a freeze plug and will it be hard to replace?
also smell fuel fumes around the gas tank after I fill it. I have to stop at the click or the fumes come back when filling. Could this be a gasket at the top of the tank? There is no leak as we have checked all the lines and such

thankyou