Christian Missions in Persia. Christianity was introduced in Persia in the Parthian period, and several bishoprics were established there (Latourette, II, pp. 263ff.).
You will likely pay more for the exchange, even if your tank is completely empty. An empty 20 lb tank will hold about 4.7 gallons of propane. That is $18.47 at $3.93 per gallon, which is the low quantity price (I just paid $3.44 per gallon when filling several tanks). The exchange is about the same price. Keep in mind this comparison is as if the exchange gives you a FULL tank.
Shopping for a propane tank: 1  Used propane tanks are often sold on craigslist or other sites for anywhere from 75 cents to $1.25 per gallon capacity ($375-$625 for a 500-gallon tank), depending on local prices. 2  Check with local propane dealers about costs and requirements for testing and certifying a used tank. (Minimums vary by location and tank size, and can range from 100-1,500 gallons.) More often, the propane company charges a fee of anywhere from $25-$250 a year but averaging around $75-$130 annually, depending on local rates, the size of the tank and whether it's aboveground or underground.