plug the roof vent and you can fill the bowl to the brim, if it does not stay at the brim you have a leak in your drain system.
carefully placed TP will wick bowl water up over the stain(s) TP can also be carefully placed and drenched with the cleaner of choice If you're really lucky you can just flush and not have to scrub at all.
Shop vac also saves the day with a 275 gallon full oil tank with a leaking valve at bottom, in a basement! Vacuum attached at top fill with no air leaks ( used duct tape). Turn it on. Piping at bottom can be removed and replaced with no leaks I did this twice on 2 different tanks amazing how well it worked!