I don't remember for which years this works, but it was discussed recently on the list: the filler cap for the rear washer fluid will fit some years. 

You could also try the rubber expandable drain plugs that are used on oil drain plug holes. I've seen a couple of styles. You'd just have to be very careful that you didn't tighten it so much that you broke the plastic in the tank. 

Ed Duntz in CT

> 
> I'm in the middle of a trip, and I just found my water tank dry and
> drain plug gone. I'm in Banff, and was going to head into the rockies
> in a day or two.
> 
> For a permanent solution I will order a real plug with the right thread.
> 
> Question is: Is there some non-destructive solution I can use to have
> water in the tank for the next week?
> 

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