It is not uncommon for me to find a gas line sediment trap that has been installed wrong. This is usually the first thing I look at when approaching a gas water heater. If the sediment trap is wrong, my spector senses tingle, and I look for other problems with the water heater. My spector senses are usually right.
When looking at the photos below, keep in mind that gas is usually very clean, and there is not that much, if any sediment in gas lines. The sediment in the photos is exaggerated for instructional purposes.
One last tidbit of information worth noting. Although not visible in the photos, the sediment traps are AFTER the shut off valve. If the sediment trap ever actually gets serviced, the technician can shut off the gas and open the trap. If the sediment traps were BEFORE the shut off valve, all of the gas in the house would need to be shut off in order to service the trap. It’s not a huge deal, but it is one of those things that make my spector senses tingle