What's the capacity of the rear tank on a dual tank '87 E150 302 van?

 

22 gallons. you can find up to 40 gallon replacements for the rear tank (deeper), but they are not cheap...

 

I recently took a long trip and filled up both tanks (i rarely do this, seeing as our '84 E150 5.0 is only a band van, mostly for local shows). I'd agree with packlet because the rear tank was reading about empty and I squeezed 20 gallons into it.