I installed an FP100 on my truck a few months ago - so far so good - it seems to work well. But I do have a question - how much liquid should I be draining from the fuel/water separator before closing it? It seems that if I let it continue draining unabated, it could drain the entire darn tank. I sure hope no one decides to be funny and unscrews the drain cap under my truck one day - with a full tank of fuel on board I'm sure I'd be a hazmat incident...

 

I drain about a cup into a clear container. If no dirt or water, shut the drain valve.