you could leave it open if it's high enough and you don't think water will get in it. THe old skool method is one of those inline gas filters. later 60's or 80's had a small tube (like a foot) with a check valve. you could always use that in the end of your tube if you use the same dia.
See you on the trail
Couple o' FJ40's, BJ70, PZJ77, UZJ100, TDI