Well, we installed a new section of 3" ABS drain line on a project which added a shower, moved a toilet, and added a double sink vanity. The old cast iron was shot. In our excitement to finiah the project after the glue-up, we backfilled and laid down new concrete (with wire mesh). Oooops. Now, we are faced with leak testing after-the-fact. I think we can insert a balloon through the toilet EL, down into the new section, and leak test the upstream fittings. Make sense to you?