Ben, When you say "dirt leg" I assume you mean drip leg. No matter how you say it, weather it is code or not isn't really the issue. As you stated, we are not code inspectors. Drip legs are recommend to be installed near each gas fixture in order to catch pipe shavings, dirt, ect. before entering the gas valve. You may wish to state in your report that they are absent, what purpose they serve and state the implications of not having them installed. However, you are not required to state any building codes in reference to any component. FYI: Last year during an inspection, the gas company arrived to the home in order to turn on the natural gas meter. He took the cap off the drip leg in order to bleed the air from the gas line and light the water heater's pilot. I was surprised when he removed the cap there wasn't any dirt or debris in site. I questioned him about how clean it was and if this is common, and he said yes. In a nutshell, he pretty much said the drip legs are useless and it isn't a big deal should they not be present. I do believe knowing the building codes is very helpfully for us home inspectors, particularly when inspecting new construction. The CodeCheck books are incredibly useful. I recommend having it on hand for reference, but I do not recommend putting the word "code" anywhere in your report. Robert