I think that a suitably sized washer (big and thick - unlike Paul) held with vice grips would work well for tightening those. As far as "how tight" . . . there is an aluminum seal washer under them, correct? If so, they need to be fairly snug, but not Popeye-arm tight. If you can't get them to seal dry, putting a little Permatex aviation gasket sealer on the washers works very well. I use this stuff all the time for similar seal rings and so forth. You can get it at most any auto parts store, and probably for a lot less than the price in the Amazon link. BTW - the fluid stays usable in the bottle for many years (think indefinite shelf life).
Amazon.com : Permatex 80019 Aviation Form-A-Gasket No. 3 Sealant, 4 oz. Size: 4 Ounce Model: 80019 Car/Vehicle Accessories/Parts : Car Electronics