Open the 80% vent valve on the westy tank, it'll fill right up without
a pump. You really only need a pump if you have a crappy auto-stop
valve (which should be replaced anyway).  I used to fill my father's
motorhome LPG tank 5 gal at a time by "borrowing" a BBQ tank full from
the lumber yard I worked at (our lumber trucks ran on LPG).

> Here ya go.
> As soon as the pressure equalizes between the two tanks the fill up will
> cease.
> 
> So you'll have a half of a BBQ tank and whatever the Westy tank took.
> The brakes on the fill up are now set.
> 
> You'll need a pump to overcome this  equalization phenomena.
> 
> Now your spending the $2900.00
>