NO sealant should be used on threaded tank fittings..sealants make removing the fitting difficult if not impossible to remove. Ralph almost got it right: just wrap the threads in plenty of Teflon tape. But no Permatex.
And when you screw in the fittings, tighten no more than one turn past hand tight plus enough to aim a 90 or 45 where it needs to go. Tank fittings are NPT standard, which means they're tapered--so slightly that it's impossible to see that they are in the short fitting. Over-tightening puts strain on the female "collar," causing it crack...not always immediately, sometimes it can take up to year depending on temperature variation.
Oh...it's much easier to get hoses onto fittings if you warm the hose slightly (I always used a blow dryer) and lube both the inside of the hose and the outside of the fittings with a little dishwashing liquid, or better yet a little K-Y, which is a surgical jelly that's water soluble, so it dries out instead of leaving you with a permanently greased connection.
--Peggie