I know of two. One is a fine material covering the fuel pick up in the fuel tank. And the other is a cylinder located inside the drivers side chassis rail. From there the fuel goes straight to the fuel injectors.
'99 beetles are fuel injected. Problems can be from clogged injectors or filter, faulty relay, or fuel pump. I am experincing the same problem on my '99 and have it narrowed down to, in my case, either the relay or the pump.