As long as the petcock seals are all good, you should be fine. I do it pretty regularly. The vacuum hose uses the air pulse from the intake to open up the valve in the petcock, allowing the fuel to flow. If it still leaks, you can leave the fuel line on the tank and stick something clean in the end of the line to plug it. Shorty screwdriver, shouldered bolt, a punch...as long as it fits just snug into the line, it should keep your floor clean. You can even use the hose clamp to hold whatever your plug is in place. Just try not to use anything that is dirty or will cut up the inside of the fuel line.
